DSLRs often have the ability to store both a JPEG and a raw file.
Given that the primary benefit of in-camera JPEG over raw is the smaller filesize, and that JPEG+raw is going to store even more data than raw alone, it seems like you're just wasting space on your card and making your workflow more complicated if you store both.
Why bother storing both JPEG and raw in camera, instead of just a raw file?
I am an amateur photographer going semi-pro and even though I still only use RAW I have come across a few occasions where RAW+JPEG was needed (or at least would be a great convenience):
In general, JPEGs are for fast preview on other devices (other than your camera) while RAWs are for editing.
In the RAW+JPEG workflow, JPEG is what you shoot for. RAW is the safety net.
The primary benefit or JPEG is not smaller files (that's the second), it is that JPEGs are actually images. Images have advantages over RAW files, already mentioned by others: quick preview, ready to email, no processing required, etc. Once the shot is taken you are done if you did things right.
I shoot JPEG + RAW because my camera produces really good JPEG output. It has flexible control over tone curves, color, and contrast. I'm not usually interested in producing HDR-compressed images — in fact, I often prefer a high contrast look which reduces dynamic range. If I get the exposure and other settings right, I really don't benefit much from RAW.
If I make a mistake with white balance or am in a tricky situation, I have the RAW file to take advantage of. Most of the time, I develop that in-camera, using the built-in tools to do so, but in the cases where I'm not satisfied with that, I use RawTherapee. (My camera allows adjustment to the color of the LCD; it's not completely color profiled, but it's basically neutral, so I can trust my eye well enough.)
I know that some cameras only allow highly compressed "Basic" JPEG in combination with RAW; mine lets me save JPEGs of any quality, and in fact, I usually use ★★★, only increasing to ★★★★ when the scene needs it or when the image appears particularly special. (See Is it worth using the Premium JPEG quality setting?)
And, in fact, in the interest of keeping my lifetime data load sane, I only keep the RAW files for those particularly special images. I know this is verging on sacrilege against the conventional wisdom, but I haven't regretted it yet. If I had paying customers, I'd definitely archive it all, just in case.
There's a couple of benefits that spring to mind, especially for portraiture work:
Speed of generating proofs - if a client is only going to pick 5% of shots for final use, there's little point in going through and white balancing everything, and then batch processing them to JPEG for the client to peruse.
Instant back-up - if a card starts to fail, you might lose a file, and you instantly have a second backup, albeit with different fidelity (admittedly the 1D allows you to write files to two different cards at the same time)
Usually people do store in both formats to save their time (as they think), in case if JPEG is ok.
But I prefer to store only in RAW. All pictures without any problems (WB, expo, contrast, etc..) I convert in batch processing, in one-two clicks. The benefits are:
There are several reasons to shoot RAW and JPEG:
Just to recap:
What you see on the screen of your camera is the JPEG interpretation of camera, depending on your settings.
My reasons to shoot RAW and JPEG:
Using Modes to get "useful" JPEGs:
However, my answer is heavily influenced by my Fuji X-E2 camera, which produces great JPEGs. I used to shoot with Sony and Canon Cameres before. But their JPEGs had been no option for me these days. To be fair, I have to admit, they had been older models.
Depending on your camera, there might be a good reason to shoot JPEG + RAW even if your workflow is RAW-only: accurate on-camera previews.
Some cameras work like this (IIRC, I have seen this behaviour at least on Canon PowerShot S95):
If you shoot RAW-only, the camera will store a low-resolution preview JPEG inside the RAW file. If you preview images on your camera, it is only able to show the low-resolution JPEG. If you zoom in to make sure it was properly focused, you will always see blurry pictures.
However, if you shoot RAW+JPEG, the camera will use the high-resolution JPEG file for previews. This way you can actually use your camera to check if the focus was correct or not.
Now you can choose between two options: a bit more space on your memory card (RAW) vs. accurate on-camera previews (RAW+JPEG).
With Canon DSLRs you do not have the same issue, as the preview JPEGs that are stored in the RAW files are of a high enough resolution.
I shoot JPEG + RAW when I use my older cameras with bad displays such as the 1Ds mk II. The display of that camera is almost useless (but the image quality is great) and I need another way of quickly confirm that focus is correct etc. I use a WiFi enabled memory card to transfer the JPEG:s to my tablet for quick review and then I import the RAW files to my computer for editing.
My understanding is that the convention of RAW+JPEG started early in pro digital photography (like Sports Illustrated at a bowl game) when computers were slower than they are today and RAW file tools more cumbersome to use. The idea would be that Photo Editors would look through the JPEG files to find the shots they needed. They then sent the corresponding RAW files to the technicians who would convert and tone those images. It assumes a multi-person workflow.
That said, a lot of news organizations just used JPEG files -- especially when they had to transmit files on deadline over a land line modem.
There are many good reasons here, but here are some other reasons I can think of.
There is DNG and TIFF/EP that aim to standardize RAW files, but very few cameras have adopted these.
If for whatever reason the RAW files aren't supported in future software, maybe because the cameras at that time is considered obsolete, you will at least have a JPEG image until you can obtain those RAW profiles.
Saving both does use a lot a disk space. There are other options, however, like online services, DVDs, tape (if for some reason you have one). If you archive your RAW files it's best to have at least two copies and one off-site so you don't loose your RAW files if your hard drive or DVD holding them dies.
Other Notes: If you want to keep both files and are worried about camera support in the future you can always convert the RAW files to DNG files. The idea behind DNG is that it's standardized, so companies like Adobe will continue to support the format 'forever'.
If you use a tool like Lightroom you can automatically have JPEGs, PNG, DNG, or any other format automatically generated with whatever adjustment/processing profiles you like. This saves space on your memory card, but it doesn't take into advantage of the develop processing on your camera. That's done in Lightroom at that time.
I've suggested RAW+JPEG to photographers who are fairly new to digital photography and are ambivalent about switching to a raw workflow, because they don't have raw-capable tools or are worried about the effort involved. I point out that they can keep using the JPEGs like they always have, but the raw files will be there, like a digital negative, for whenever they're ready to work with them.
In my opinion, it is about ease of editing and space to store them. I shoot raw because it give me for flexibility to post edit my photos. After edit, I export to JPG and delete the original raws.
Take a look at this size comparison (same photos)
22M IMG_9277.dng
22M IMG_9279.dng
22M IMG_9281.dng
22M IMG_9282.dng
22M IMG_9283.dng
22M IMG_9284.dng
22M IMG_9285.dng
22M IMG_9286.dng
20M IMG_9288.dng
20M IMG_9290.dng
21M IMG_9292.dng
21M IMG_9293.dng
21M IMG_9294.dng
21M IMG_9295.dng
300M total
2.2M IMG_9277.jpg
2.5M IMG_9279.jpg
3.0M IMG_9281.jpg
2.7M IMG_9282.jpg
2.1M IMG_9283.jpg
2.6M IMG_9284.jpg
3.5M IMG_9285.jpg
2.8M IMG_9286.jpg
2.5M IMG_9288.jpg
2.5M IMG_9290.jpg
3.1M IMG_9292.jpg
3.3M IMG_9293.jpg
3.4M IMG_9294.jpg
3.5M IMG_9295.jpg
40M total
I think it only worth to keep raw for very special photos.
As a professional photographer I rarely need the jpeg files so I only turn them on when needed. When I do need them it is because I need a fast edit and raw files require a bit more processing time and CPU power than the average laptop can handle.
For instance I went to photograph a luncheon for a company where there was to be a few big name people speaking. When I arrived the contact told me he was told at the last minute that he needed a quick turn around on 5 of the images... a couple hours instead of having the entire shoot ready 6 hours to a day later. I turned on the raw + jpeg so I would have the ability to grab the jpeg quickly and do a quick edit and supply him the file quickly after the event when I got back to the office.
I've also had it where there were times when I could download the disk of images right on site when the client changed the deadline. They could have an untouched file immediately after shooting it, and they wouldn't need Photoshop, Lightroom or whatever program to convert a RAW file into something they could use.
Speed is the main reason to use Jpeg (size is another one). The reason to use raw is because it gives more latitude for adjustments and a wider color space, although the new jpeg revisions that just came out could make the wider color space a moot point.
In-camera .jpg produces more accurate colors. At least, that is my experience, especially with artificial lighting.
For an example where post-production converters failed, see here.
Not only did Lightroom fail, but the raw converter from the same manufacturer could not even produce the right colors. I was really glad I happened to have raw+jpg enabled that day.
I have since tried to remember having jpg+raw enabled for artificial/stage lighting from then on.
I don't know the actual reason for JPEG/RAW mode, but it's the mode I use most of the time.
Occasionally somebody asks me for a particular photo, and it's easier, faster, and more convenient to give them the JPEG than to load it on my laptop and edit in LightRoom or Capture One.
RAW + JPEG is also nice because sometimes the out of camera JPEG is "good enough," though I'll usually tweak it a bit anyway :-)
It can also be nice to compare how I've processed the file versus how my camera saved it as JPEG. Capture One and LightRoom support for my camera (Fujifilm X-Pro1) isn't great, and the camera's built in presets (Velvia, Standard, ...) aren't select-able in the apps, like they are for some cameras. Having the camera's JPEG along with the RAW lets me compare what I saw on the camera's screen with what I've done in the RAW processor.
