This controller connects to the GameCube port of the Wii or GameCube. It is essential for ALL GAMECUBE games and can be useful for certain games Virtual Console (Wii) WiiWare and Wii (Smash Bros. Brawl for example). It has a long cable (3 meters or less), is robust enough (quality Nintendo requires). And in the case of a wired controller, there is no need for batteries!
Personally, it allows me to play the best GameCube games on Wii (Soul Calibur 2, Mario Kart: Double Dash !!, F-Zero GX, The Legend of Zelda: The Wind Waker) and I am very happy! :)