Imagine an enemy passing out of sight and still being able to shoot him by pointing your controller where you'd think he'd be in actual 3d space. Imagine running in the opposite direction of an enemy (in game of course) and being able to point your controller behind your back and shoot him. Imagine not having to place a stupid infrared sensor next to your television. This type of gaming could be delivered without the use of such primitive technology.
[Edit: I don't know whether or not you could pull this off with the Nintendo Wii because I still don't know everything about it, but it's certainly possible with existing technologies which I'm pretty sure some of the Nintendo Wii houses. I'm pretty sure the Wii knows where the front of the controller is in relation to the back of it because of the way the bat supposedly acts in Wii Sports. So with that in mind the above gaming scenario is entirely possible with an extra location marker or two.]