I have found in iOS 9 (don't know if this was also happening in iOS 8) but looks like video ads in games and other apps are caching and causing app sizes to inflate like crazy. Every time you watch an ad or are forced to watch an ad the apps are not getting rid of that cache. At least if it opens in Safari you have the option to clear cache. Usually some app like Battery Doctor or PhoneClean or something along those lines used to clean these out but now that iOS 8.3 and greater are preventing access to app sandboxes looks like there is no way to get rid of this extra junk except to uninstall and reinstall the app. Any suggestions? Can't believe Apple is doing it this way. Why offer 16GB phones if you inflate app sizes with all this unnecessary stuff.