We generally book a hotel and parking separately, but last time, we found out the hotel we were staying at (Comfort Inn Toronto Airport in Mississauga) had a park sleep fly option at check in, so we gave it a try. It was fine. We ended up missing the shuttle we were supposed to take (we have a toddler, so didn't get there 15 minutes early like they told us to, but the shuttle also left early, since we were there before the scheduled departure time), so had to wait half an hour for the next one. I don't know that I'll bother with it again, since I don't think we saved enough to make up for having to wait around for half an hour.