I've practiced on several (four IIRC) 12 footers and most noticeable to me is on long shots, you can lay out closer to horizontal and possibly more relaxed than on a 9 footer where nearly all the shots are jacked up to some degree.
Speaking of being jacked up, this is one of my favorites. Your bridge hand resting on the rail above the corner pocket and your arm for your bridge hand has nothing to rest on.