Buying entry in advance eliminates the need to queue for the ticket booth before entering the event. There will be a seperate queue for pre-booked entry in the morning, which often moves faster than the standard queue.
The doors will be opened for all early entry queues at 9am on Saturday and Sunday. For the Friday Preview all ticket holders will be able to gain entry from 6PM.
This ticket will then be exchanged for admision when you enter the event.