If I'm not behind you I don't have to worry about you kicking up rocks onto my car, waiting for you to get off your cell phone at the light, I don't have to slow down because you can't handle taking a turn at the posted speed, ect. Yeah, I'll be the guy in front using my gas for enjoyment and open road. If I cared about fuel economy, I'd drive a prius.

I just like to go zoom :(

That said, I slow down to overtake other cars, or around other cars in general.