How useful/effective the app is, and excessive battery use. I try a lot of apps; there are some that I really like, some that I really need, and some that just catch my attention for various reasons. I backup all my apps using titanium so there's no issues with uninstalling an app I may want to use at a later date, but unless an app is really ineffective it tends to stay on the phone for a while. A prime example is Facebook, which I don't need on a mobile basis and has always taken up a fair amount of memory and used a fair amount of battery.