TFOX, I can definitely see this as an advantage on some designs. I've owned bows, where the limb pocket was the only thing keeping the limb from moving - a very poor design. However, with the use of rockers and/or pins, the limb pocket can be made irrelevant. About the only purpose would be to keep debris from easily wedging between the limb and the riser. Rockers and pins will anchor a limb so it's can't move.

In every design, the butt of the limb presses against the limb bolt, not the limb pocket. On the other end of the pocket, is either a rocker or some cushioning for the limb to press against. With or without a pivoting limb pocket, the limb is still in the exact same position. The pivot point of the limb still remains the same. Making the limb pocket move along this pivot point simply can have no effect on efficiency that I can imagine.