When I first saw this feature over a year ago, I understood completely that this would be one of the most important features in the v8.5 release. DAOS basically allows you to move all file attachments from all databases on a server onto a separate filestore. All of a sudden, only one copy of a particular file is kept per server, instead of hundreds of copies in each mail file. All of a sudden, Lotus Notes databases are databases again, and dont have to bloat with file attachments.
This is important. Go off and read this article on DAOS here, print it out, and use it a a very strong case to get your server estates upgraded to Domino 8.5 as soon as your organisation is comfortable. Its going to save you a *lot* of money.