Video game controllers have been gaining buttons for years.  We started with a single action button, moved up to two buttons in the 8-bit era of the Nintendo Entertainment System and Sega Master System, and so on until we've arrived at the ten buttons monster that is the DualShock 3 controller for the Sony PlayStation 3.  The first example of "button creep" that I remember striking me in a "why do we need this?" way has to be the Super NES's L and R buttons.  Located on the top of the controller, it took a while for these two buttons to find their purpose.  1UP's Retro Gaming Blog seemingly agrees in an article that calls these shoulder buttons one of gaming's noblest failures.

The problem is, no one's quite sure what to do with the L and R buttons. Their placement makes them convenient for auxiliary inputs but impractical for commands executed in the heat of action. The player's index finger rests on them, sure, but their arrangement is such that it's difficult to squeeze off quick actions like you can with the classic thumb-on-the-face-buttons approach. The shoulder buttons look impressive and bespeak a machine with incredible power. But what on earth are they for, really? In 1991, it was a mystery.  Just because Nintendo wasn't sure what to do with the shoulder buttons, though, didn't mean they didn't give it the ol' college try. And so they made a sporting effort with the system's flagship launch title, Super Mario World. By pressing the L or R triggers, players could scroll the screen ahead (or back) very slightly to get a glimpse of what lay in store (or behind). 

It was a clever idea... and it was also practically useless. Peeking ahead would be a big help in games with arbitrary pits and unfair hazards, but the rub is that this was Super Mario World; it was better than that. The game could be challenging, but it was never cheap. Danger was always properly telegraphed. The peep maneuver wasn't even much help in the auto-scrolling stages, because activating it was too slow and cumbersome. It was, in short, a completely unnecessary feature -- a real rarity for a game directed by Shigeru Miyamoto, who normally takes a "lean and mean" approach to design, culling any feature that doesn't make a significant contribution to a game's overall design.

Admittedly, the L and R scrolling gimmick in Super Mario World didn't do much to boost the gameplay.  The first game that I felt actually used the shoulder buttons for something useful is 1993's Mega Man X in which X's special weapons could be turned on and off without having to stop and navigate the pause menu first as in previous Mega Man titles.  Not having to stop for a weapon change helped keep the action moving, and although it's a little thing, it was one of the elements that made Mega Man X a bit more frantic than its traditional Mega Man franchise counterpart.