Usually it all deals with how you want the airflow going around the car it depends on the nose. You need to direct some of the air to the diffuser and some to other parts of the car. Also there is a increase of downforce (more surface area) but not much drag associated with it.
Simon: Nils? You can close in now. Nils?
John McClane: [on the guard's phone] Attention! Attention! Nils is dead! I repeat, Nils is dead, ----head. So's his pal, and those four guys from the East German All-Stars, your boys at the bank? They're gonna be a little late.
Simon: [on the phone] John... in the back of the truck you're driving, there's $13 billon dollars worth in gold bullion. I wonder would a deal be out of the question?
John McClane: [on the phone] Yeah, I got a deal for you. Come out from that rock you're hiding under, and I'll drive this truck up your ass.
