I am an iPhone user, but I am sure this functionality is also available for Android:
The phone can give an alarm when I reach a location, for instance the city of Amersfoort. I can also set the distance, after which the alarm is triggered, e.g, 6 km around Amersfoort, or 20 km.
What would be nice is, that this feature works more generalized. Suppose, I am visiting another city and I need to buy something in a drug store, but I do not want to change my schedule for that. It would be nice then, that my iPhone warns me, when I am in the neighbourhood of a drug store.
So the little alarm is then triggered to a category of locations, in stead of an exact location.
Make it so, Apple, you can thank me later 🙂