I knew this had to be a trick question because I couldn't see why MS would add that command. As Tom said, rolling back a rollback is nonsense. Being April Fool's Day helped with my answer decision too. :-D
Actually I think I misread the question (actually I diodn't bother to look at what the command was supposed to mean, and interpreted it as meaning something else - that kind of mistake is even siller than misreading - but it made no real difference.