Do you mean the slight bat tail?..
IMO.. it does nothing much..

If it was a swallow.. diamond.. or a square.. and if most people were asked what shape it was by just surfing and paddling it without looking back there I'd bet a million dollars 99% of people couldn't tell what shape it was back there.. Naish know what they're doing so I'm guessing they did it for a reason.
I think maybe it's more a fashion or modern look thing.. It probably has a better release than the older squash shape so you might get a slightly fast turn.
Flame away those who don't agree..