I am also curious about this. I've set up a space for our Compliance team, but they want to do more than just recreate the current site they have on our intranet. Would be helpful to know what other companies are doing!
I've seen companies use Projects to handle contract redlining and approvals in secure Spaces & Groups. They use Tasks to manage the handoff process, and the Microsoft Office integration has been highly useful for version control and document collaboration. Since everyone wants to know what the status is with each contract and who it's currently sitting with, creating individual Projects for each contract provides a transparent way to show that type of information.