Also if you want to go home now, or go to the store now and it's rented out by some one: you're basically fucked.
You can program a range limit and certain hours (be no farther than 30 miles away by 4pm and not in use) sure but when anything unexpected comes up (on either end) you don't have a car for X period of time.
Even just sharing the car has this problem, oh it can drive back home empty, but the logistics of making sure it can drop Bob off drive home get Alice drive her some were pick Bob back up up drop him at home in time to go get Alice are only barely more convenient than "sorry I need the car today" for twice the mileage cost natch.