It's been pretty well documented that overeager, sweaty-palmed Wii players are prone to flinging their Wii-motes every which way, often destroying property or people in the process. Sure, Nintendo recalled their originally-wussy wrist straps and replaced them with slightly beefier ones, but that doesn't go all the way in solving the problem.
This is more like it. The Retractable Wii Sports Cuff keeps that Wii-mote securely attached to your wrist at all times, so even if you let it go in a fit of tennis-fueled ecstasy, it won't fly off and take out someone's eye. And for only $6, it's cheaper than any kind of Wii-related insurance you might have been considering purchasing, so it just makes sense.