People joke about using paper tickets
However they now have it where you have to enter your registration plate for those, too!
It used to be the case that you’d not know how long you were going to be, so you’d pay for 3 hours parking. When returning to the car with an hour still on the ticket, you’d give that to someone who was just arriving in the car park, good deed for the day and all that (and sometimes you’d be the recipient of the ticket).
However this community spiritedness meant that parking spaces were only being paid for once within a given period, even if multiple vehicles had used that space.
So pay & display machines changed to include the registration on the ticket so that you couldn’t pass it on if there was still time left on it :(