Have you ever been out and accidentally left something behind? What if there was some way of knowing as you leave that you have forgotten it? Thats exactly what Left Behind is for! Add the item to the list, set a location, and a distance of how far away from that item you have to be before the app will notify you. As soon as youve walked a certain distance youll get a notification saying "Dont forget your jacket!" or something similar depending on the item.
Location services are used in the background to check whether you are out of range of any added items and notify you if you are.
Continued use of GPS running in the background can dramatically decrease battery life.