Google Drive has an application data folder that is a separate permission from reading and writing all your files: https://developers.google.com/drive/web/appdata
Again, that means a user cannot drop their files into a special app folder for processing. It does not facilitate the simple use case of creating an App to distribute purchase orders to vendors.
That's also not what the parent comment I commented on was referring to.
I think it is obvious that purchase orders are an example. Have temporary hidden storage via an application data folder may be useful, but I am talking about folder level permissions for an app.