We primarily use EXIF to automatically determine when your photo was taken, so it can be added to the correct slot in your journal.
We also read focal length, exposure time and similar settings so they can be displayed in your entry. This allows you to search your entries by camera manufacturer, for example.
Additionally some cameras and phones record the location where the photo was taken. With your permission, we can use this to display you entry on a map - find out more about this here.