Why does Quirrell want Harry exposed to Dementors?

At the risk of building this theory on top of another unconfirmed theory... It's been speculated that Quirrell himself is Demented. He doesn't appear so when Voldemort is telepathically controlling him, but when Voldy takes a cigarette break or whatever Quirrell enters zombie mode. Quirrell is just kind of an empty body, zombie-like unless Voldemort is logged in.

Maybe Voldemort wants to control Harry's body in a similar fashion. What the difference is between dementing and then telepathically inhabiting, versus simply using the Imperius Curse... /shrug.