That's a perfect one-word answer from Hc4361but I'll just add a relevant point:
Parking wardens may sometimes needs to wait for a certain length of time to ensure that the driver can't find a way of contesting the ticket.
For example, if a driver has parked his car where there are valid waiting restrictions but no valid loading restrictions, he might have just jumped out of his car to collect bulky pre-paid goods from a nearby building. If the warden simply issued a ticket and walked off, the driver could challenge that ticket on the grounds that he was 'loading', rather than 'waiting' (even if that wasn't actually the case).
So, where loading is permitted at the relevant time, a parking warden would be wise to wait to see if the driver returns within a minute or two, carrying a heavy or bulky load. It's likely that the warden's employers would instruct him to do so. (However it's not a statutory requirement). But where both waiting and loading were prohibited, there would be no need for the warden to wait.
Chris