Answer:
It helps to give the geographic location of photos.
Explanation:
A geotag is added into the photography information when it's taken. That info is part of the EXIF information of a photo that lists a bunch of data related to the photo, like the camera brand, model, the aperture, the speed, the ISO, and so on.
That's assuming the GPS info is available of course, but if it's taken by a phone, it has the GPS info. Most mid-range and upper-range cameras have it too.
That information is used for example by Google Maps to present photos taken at a specific location.
