I'd bet on the occupant of the unit -- they may be trying to prevent others from using the spot, to reserve it for guests or for their own use if the do a ZipCar errand, or whatever else, even though they're only actually paying the landlord for use of the home. People are completely insane about asserting ownership over parking adjacent to their residence. You see it all the time with folks getting mad at others for parking on the (publicly owned) curb in front of their homes.