The fist question needs to be 'What are the legal requirements for document retention in the jurisdictions and disciplines you perform work in?" And that a one that needs to be answered by your corporate counsel, not cad staff, designers, or engineers.
Def. good point. We have a couple documents that are hard copy in the 'fire room' due to legal requirements.
We have actually had document management unilaterally decide to destroy active documents so we are kind of un-trusting to them at the moment.