At T-4 minutes they hold for 10 minutes and the commentary said this was planned beforehand. Does anyone know why they don't just plan to launch 10 minutes later without the 'hold'?
The hold is also used as a sync point between all of the different activities that have to be completed at certain points in the launch preparation. For example, at the t-4 hold for the Curiousity launch, they needed to pass the go/no-go from the entire team. If one team had been running late up till that point it wasn't a problem, the other processes just entered the hold earlier. Once the last hold has been cleared, all of the remaining processes have to stay synchronised.