A lot of cameras (especially on your phone) offer the ability to tag your images with GPS information.
To this date, I haven't really found a "killer idea" that would convince me to add GPS information to my photo. Is there any generally good reason, or is it just some kind of niche tool?
I bought a separate GPS unit for my camera and use it extensively. Actually, I keep it pretty much permanently attached on the hot-shoe mount and have my pictures geo-tagged by default. I have a hard time imagining why you wouldn't want it.
I take a lot of outdoor pictures and am anal about keeping records. For years before I had this camera, I'd look thru maps and figure out where each picture was taken when I got back, and record the lat/lon coordinate. It is so much easier and nicer to have this done for me automatically.
Another side effect of the GPS is that the camera clock is always accurate. My camera sets its clock from the GPS whenever the GPS has a fix. This is often enough that the camera clock is effectively spot on all the time for my purposes.
With a GPS, every picture then really records where, when, and what it looked like. Ways I've used that, or reasons I've found it useful include:
I had the reverse experience when my car got stuck behind a large tree that fell across the road deep in the national forest 20 miles southwest of Flagstaff AZ. This was before I had a digital camera with a GPS unit. When I got to the police station, I pointed out on the map where the fallen tree was. Their first reaction was "No, you couldn't have been there. Nobody goes there.". I had to argue with them for a while and explain landmarks I passed before they (at least pretended to) believe me. By the time I did get back to the car hours later, the fallen tree had been cleared, so in the end something worked. A single picture with lat/lon coordinates would have been really useful though.
As Knob Scratcher pointed out in a comment, the location data in a picture file might give out information you don't want everyone to have. Actually, this is the case for all meta-data. Time and camera type are also things you might not want everyone to know.
So don't give people pictures with meta-data. The camera includes a lot of meta-data in the raw file. That has to be processed anyway. I have my software create JPG derivative files that contain no meta-data at all. Don't give out your raw files. Many people wouldn't know what to do with them, and bad post-processing will may you look like a bad photographer, not whoever did the post processing.
I do have my picture archiving and indexing software grab various pieces meta-data from the raw file and associate that data with the picture. The pictures and selected data is written to a HTML tree for easy viewing, navigating, and being able to display annotation with the picture. The software that exports selected pictures from the large collection can be told what type of data to export with the selected pictures. This way I can control what the rest of the world gets to know about each picture. So far this has worked well.
In addition to the points already mentioned, I would add: for posterity. I'm probably more curious than the average monkey, but there are family photos from when I was a kid (or earlier) that I wonder about the location of, and there isn't always somebody around who remembers.
It can also come up in other cases where people are looking at old photos that they didn't take themselves... like this one.
In my opinion, it's a niche feature for architecture and landscape photography – to keep precise track of where the photo was taken. And to be able coming back there again if necessary – it's pretty easy to find some address in the city, but way harder to find the same rock or path somewhere in wild..
and it can be useful in general:
A negative "benefit" is privacy compromise. Many people aren't aware that the images they post on line may contain GPS information in the "Exif" metadata, added to the file by the camera. That's not necessarily a good or a bad thing, but something people need to know about. Fortunately most social media sites such as Facebook will strip the metadata.
As @Knob Scratcher noted in a comment to another answer, it can give potential thieves a clue about where to find your valuable posessions.
1) It could be useful for keeping track of where you are. Now that the per-shot costs are negligible these days when playing tourist the first thing I do is snap a picture of a sign indicating where I am. GPS could serve a similar purpose.
2) I have a GPS-enabled camera. It's a real battery hog and takes long enough to acquire that I almost never use it but a couple of years ago I was out hiking and found a spot the rangers needed to fix. I snapped a few pictures to e-mail them--and pointed out it was geotagged so there was no question exactly where the tree was blocking the trail.
