It's not really a game concept but an idea for controller buttons, hence the title.
Well, if anybody is familiar with the racing controller made by Interact that has a wheel on top of the thing that you can turn, and looks skinny, it also has a trigger beneath where when you push one way, it triggers the 'A' button, and if you push the opposite, it triggers the 'B' button, for example. I think this feature should become a standard feature on controllers as a shoulder button, with "pressure sensitivity" of course.
Example of its usage? I tried playing Monaco Grand Prix on the Dreamcast and found that one button was used for gas, the other for brakes. So why not combine the two into one button? And the other button could be used to change gears, too. ;) I don't think its use could be limited to racers, like fps's could used it to scroll through weapons or use as a secondary firing mode.
I think developers could be more creative with its use. However, I think there is a downfall in that there could only be two of them to be comfortable, since if you're like me, my middle fingers aren't that, how do you say, dexterous. I still think it's a cool idea though.