engine - 11:54 am on Apr 5, 2013 (gmt 0)
In order to run smoothly, your app may depend on data it stores in Drive. But occasionally, users may accidentally move or delete the very file or folder your app needs to function. The app data folder is a special folder in Drive that can only be accessed by your app. The app folder’s content is hidden from the user and from other apps, making it ideal for storing configuration files, app state data, or any other files that the user should not modify.
Although users cannot see individual files in the app data folder, they are able to see how much app data your app is using and clear that data in the Manage Apps dialog.Added Flexibility In Google Drive For App Data Folders [googleappsdeveloper.blogspot.co.uk]