Parking meters may yield little or no net revenue

Question

Explain: “Even though parking meters may yield little or no net revenue, because of the rationing function they perform nevertheless be retained”

Answer 1

Even parking meters that charge, say, 25 cents an hour do perform a useful parking-spot-rationing function: the car owner must either move the car when the hour is up or rush out to feed the meter to avoid getting a ticket.  It is not money or ration coupons that ration the parking space but the timing device on the meter in this case.