It actually does have a function other than looking cool. It doesn't help to dissipate heat it serves to keep the heat IN. This means the exhaust gasses stay hotter for longer and hot gas flows faster than cool gas. This means that waste exhaust is expelled faster and generally results in increased performance. I definitely got an increase as my bike would labour hard above 100mph and now it pushes on easily to 120mph all the while pulling like a train.
