In Settings / General / Usage there is an Edit button in the Music and Podcasts apps to remove the cached or downlaoded files stored by the application.
However that option doesn't seem to be available in other apps, even if they use the Documents directory. I've read somewhere that this is a developer-enabled feature (maybe Info.plist?)
Is this something I can enable my users to do, and if so, how?
if your application download file and cache files which user want to remove after a time being you can implement the bundle setting functionality, and you can detect that change when your app launch and delete the files from your document folder.