Always keep paperwork.  You can never be sure what end-client they sent the work to and who might want additional work done or an update.  On the other hand, some same end-client might show up on your doorstep with a  claim.  In the latter case, keep your work.

A good auto-feed scanner and an extra external hard drive are a worthwhile investment to back up your paperwork and eliminate it in favor of space and sanity in your office.