What compels users to delete applications from their smartphone? An app that is useful in emergencies--a flashlight app or an emergency communication app, for example--may not generate much daily use but is unlikely to face the axe. Apps that serve little to no purpose are a different story, however. Are there tricks that developers and app marketers can follow or mistakes they can avoid in order to limit the number of times an app is uninstalled? And what types of apps are rarely ever uninstalled? Special Report