Mostly predictive stuff from Google Assistant and Maps like traffic delay notifications, search suggestions (if you go to a certain place a lot at the same time and you open up Maps to search for a location, they can 'infer' the places you're most likely to be looking for at that time and show them instead of you having to type them up), meeting reminders tied to a location, etc. GMail targeted ads are also affected (you might see more ads relevant to the places you actually visit if you keep location history on). And, of course, the timeline feature from your account (that lets you review places you've been, time you traveled, if you were running, walking, driving, etc.).