A self-driving car can drop you off at the door, and then go park itself wherever the best location for cars is in the area, and probably have no problem reserving/finding a space mediated by various parking lot controllers, and finally, since the car is both unloaded and computer controlled, be able to park in a much smaller location.

The parking location doesn't have to be close and it doesn't even have to be a permanent parking location.

Hell, a self-driving car could in fact go back home if home was reasonably close enough.

Or head over to the airport and make you a few bucks as a taxi.