With a rear mounted engine you have a major problem with cooling it. You also need to allow the engine to suck in nice cool air to maximise the power. Most car makers put vents in the rear wing or use scoops on the roof line or beside the doors to get air into the engine bay. The Aero is a monster and certainly generates a lot of heat, which explains why there is such a large vent in the side of the car. The long leading channel permits a much greater flow of air compared with just having a vent on the rear wing. Vents are popular on car styling projects but it is fair to say that most cars with front mounted engines have little real need for them. They look much better with flared arches and can also be used to aid brake cooling and aerodynamic downforce if done properly.