Magnet,
for the most part i only play classics, most of which require only 2 buttons. Alot of those games that require more than one use the 3rd (or 4th) as a special button, say like smart bomb or whatever. I wanted a button off to the side a touch on each player control for that. In practice it works really well. makes a nice place for a reverse button in defender, a smart bomb button in tempest, so on. any button that deserves a special spot on the panel due to its function. plus i thought it looked cool. and my pinky told me to put it there.