I'd say i do it for the same reason. Its not to have more HP than someone else, i'm going to college right now for auto mechanics. I currently work at a shop and i think its rather fun bolting on stuff to the engine or even hooking up various gauges inside my car. I know most of them wont' really help with anything but it helps me learn like how that works or whatever.

And then of course because it makes it more my car than just another in a parking lot.