The problem I have is I don't look through my fridge, freezer, and pantry every day to see what things are going to go bad soon. I often forget about something I have, especially if it ends up behind or under something else. I don't end up rediscovering it again until it has gone bad.
The app also makes it easy to quickly get a handle on the ingredients going bad soon so that you can think of something to make with them. I've also found myself using it in the grocery store when I'm trying to remember if something I have has gone bad or not yet.
Just searching the list to see if I even have something is very useful too. I used to end up buying something twice since I forgot I had already bought it a while ago.