Comment Re: Application sandboxing (Score 4, Informative) 577
Android does sandbox apps. The default internal directory for each app can only be read/written by itself. Prior to version 4.2, the SD card was public and could be read/written by anyone. 4.2 and later, only parts of the SD cared are publicly readable and only parts are publicly writable.
In both cases before and after 4.2 uninstalling will remove the private directory. It will also remove any private directory on the SD card, so long as the app used the default location. Some apps don't, purposely, so their data will persist if reinstalled.