Sounds intruiging..No real need other than ease of navigating.
It lets you get the viewpoint in the optimum position easier. With a mouse alone you would have to click and rotate them use a modifier to move the viewpoint angle. Then scroll in with the wheel
With the 3d mouse you would twist tilt and push it forward in one movement to achieve the same sequence of movements in one action.
I treat it as mouse for the right hand controlling the pointer and 3d mouse as my camera man with my left hand.. Far more precise than using the mouse to navigate.