I'll add a mention here in favour of marking spots, all the time, even if the spots are over-sized. I recently used a car-sharing (Mercedes/SMART fortwo vehicle) service, and parked the car reasonably, let's say 40cm front and rear. Close, but fair. Between the time I left the car, and someone being "parked in", someone had left, leaving a space, where someone had then parked nearly touching the car I left, subsequently in the now
tiny space behind the new parker, someone else parked, too close. The middle parker unable to extricate their vehicle called the police reported my car as the offender "it was nearly touching my bumper, I can't get out" leading to €370 fees from the police for towing the shared car I had used (although, a call to the provider would have rendered it unlocked and drivable), and a further €120 in fees from the car sharing service provider.
I now take a photograph of my car (or rented shared cars) in all parking situations, in the hope that evidence that "i was there first" might mean I am not subject to accusations of offensive parking when over-eager city-dwellers park in spaces that are really too small, and later find themselves blocked in.