Personally, I put a rebump on an email to someone I need a yes/no answer from. Maybe it's a proposal that needs approval. Maybe it's whether they'll be joining us this weekend for a beer (because I have to make reservations). I don't expect an immediate response, but I set a rebump for a day later (default is 3 days) because I shouldn't have to chase you down to get a simple answer.

Definitely see your point about how annoying it would be to get these one email forwards from my great-aunt, though. We are trying to convey to users that Rebumps should be used judiciously. It seems to be working so far.