I have a group interested in uploading a large (in size) amount of files to opportunities.  My concern is that this will quickly consume our file storage allotment.  

My thought was to delete the files after X amount of time, maybe one year.  However, it seems that when you delete a file from an opportunity the file remains in the files tab.  Any ideas as to a solution?

I'm a long time admin, but somewhat new to chatter files.