It is largely ergonomics, giving you more space in the boat. Also you are increasing the distance between the CB and the rudder which gives the rudder more authority and the boat less twitchy. This is more important on boats that have the CB quite far back.
I almost expect gantries to get shorter and shorter now with the use of the T-foil as it gets the lift more under the boat.
On another note does anyone want a solid purple gantry. I removed one from Primal when I rebuilt and it is on its way to the skip at the moment.