When you look at a raw file, what you see on the screen on the back of your camera or when opening a raw file with an application on another device is not "the" raw file. There's really no such thing in terms of a viewable image.
What you see is one of a near infinite number of possible interpretations of the raw data. The raw data has been processed in some way to produce the image you are seeing.
- On the camera's LCD it is almost always the JPEG preview produced by the camera from the raw data based on the in-camera settings at the time the image was recorded.
- On other devices it may be either the JPEG preview attached to the raw file or another interpretation of the raw image data created by the application used to open it based on the defaults of that device/application that opens it.
Here's what a demosaiced but otherwise unprocessed (properly exposed) raw image file looks like:
Here's the smaller thumbnail jpeg preview of the same image with the in-camera processing applied:
In general, third party applications such as Lightroom and Photoshop (which both use Adobe Camera Raw under the hood to produce the image preview from the raw data that you see on your screen), Aperture (back when it was still a thing), Capture One, DxO, etc. apply their own default settings and use their own demosaicing and processing algorithms that are not the same as the ones written by the camera manufacturers that are used internally by the camera. Most of them emulate the manufacturers' algorithms fairly well, but they are not exact matches.
Assuming no editing, what's the difference between in-camera jpegs and lightroom jpegs?
Whatever the difference is between the in-camera algorithms and in-camera settings applied to the raw data to produce an in-camera JPEG and Lightroom's algorithms and default settings applied to the raw data using Adobe Camera Raw. For some cameras (and various in-camera settings) the difference may be imperceptible. For other cameras (or particular in-camera settings) the difference may be rather stark.
One quite easily discernible example: Shoot in B&W in-camera and save the raw data. Then open those raw "images" in Lightroom using LR's default settings. When you open the raw files LR will render a color image from the raw image data. Note that in the Preview section of LR, the attached JPEG preview may be used which will show the B&W preview JPEG, but if you use the Develop module of LR with a generic profile selected it will render the image in color using the raw image data collected by the sensor.
On the other hand, most manufacturer's in-house raw processing applications start by opening a raw image file using the same in-camera settings that were used to produce the JPEG preview image. Unlike most of the third party apps that ignore much of the information contained in the 'maker notes' section of the EXIF data of the raw file, the camera makers' software usually reads and uses all of it by default when opening a raw file. These would include Nikon's ViewNX, Canon's Digital Photo Professional 4, etc. Note that it is still possible to change the settings any way you wish, but it is often nice to have the app open the file initially using the in-camera settings current at the time the image was taken.
If you use a Canon camera and open the same raw images files with the camera set to B&W (Monochrome Picture Style), they will initially be opened in B&W. But all one needs to do to see the same raw data rendered in color is use the drop-down menu in DPP to change the Picture Style to any of the color options.
What's the difference (other than time taken) between these two? Is there a (practical) difference?
Again, that all depends on how far the in-camera settings and processing algorithms are from the settings and processing algorithms of the off-camera image converter/editor. If you can't tell any difference between the two and are happy with your results, then there is no practical difference.
But for many photographers, the extra control and more options allowed by using post-processing applications with the raw image data are well worth the trouble. This is particularly the case with photos taken under less than ideal lighting, such as nighttime and indoor sports or concerts and theatrical productions.