You will notice sometimes aerodomes will hold an arriving aircraft if the bay is full. That's never happened here unless the weather is IFR, then the next aircraft to land is allowed to land ONLY when the guy ahead of him is officially clear and off the runway, for IFR arriving safety purposes. I once saw a tv ATC story ages ago that there are too many aircrafts in the air and not enough concrete to put them on, this was a quote from an American tower controller about 15 years ago.