The new patch supports the primal hunt map pack (a workaround to no longer being able to play Primal Hunt online) and throws in the custom map Broken Dream.
You won't need it for playing AvP2's default maps, but will need it for servers running the Primal Hunt map pack.
Honestly, the Primal Hunt maps should have been added to this years ago when the patch was first released. Better late than never.