Transferring Liability.
The whole point of the Third Party Vendor or having an event on someone else's property is to make sure they are the focal point of the law suit.
You will still be sued! You will almost always be sued!
But they have the brunt of liability for serving underage people and the safety of their premises. Falls, assaults etc.
You can have a lot of events if someone else is serving the alcohol and its at someone else's place.
Actually sororities have been famous for this for years. The girls party at Fraternity Houses that have traditionally provided the alcohol and the space, and therefore have taken the fall if anything went wrong . . . good move on the girl's parts
.