Airports like Gatwick, Heathrow and at peak times Stansted need both the right infrastructure and ATC procedures to minimise runway occupancy. These can include designing rapid exit turn-offs at the correct location and angle, providing RETILS at these turn-offs. It was proven through trials at Gatwick that RETILS reduced runway occupancy times.
The correct location and angle of RETs for arrivals is essential otherwise the runway is occupied longer than necessary. A 25 deg angle is considered best and for medium size types like A320/B737 a distance fo 1600-1900m from landing threshold is about right. For "heavies" the distance from threshold needs to be increased to about 2100m.
Also important is departure route after take-off which is often initially based on noise issues, so if an early left or right turn is possible with no vortex spacing or ATC airspace issues then an efficient departure flow is possible with consecutive departures turning left and right.
Another factor is general taxiway infrastructure and number of parking stands available. If the runway can cope with 40 arrivals an hour but there's limited taxiway infrastructure and few stands to cope with it then the movements have to be artificially capped so the limited infrastructure can cope. Same reason can apply for the number of passengers that can physically be processed safely through a Terminal building with customer service in mind.