This new mousepad and wrist rest allows you to mouse at a more natural position than just placing your palm down on the desk.
According to the company, normally when people stand upright naturally, the palm of the hand turns towards the body. But when people use a mouse, the palm is forced to turn to the ground as a ligament and muscle in the shoulder is twisted, thereby causing a crick and pain.
This sorta makes sense—you want to make your arms and wrists as close to resting position as possible so that keeping it there for a long period wouldn't cause a lot of stress. Another idea along the same lines would be the ergonomic mouse, which lets you mouse vertically—like the handshake position.