I believe they seal and smooth the gaps between the framerails and the front and rear bumpers, that can make a HUGE difference as much less air would be trapped under the car...

 

The reason the wing was so high on the Superbird and Daytona was so the trunk could be opened. Otherwise, it could have been half the height. Most rear spoilers are useless, but in some cases they serve a purpose. On some cars a rear spoiler decreases drag by separating the air flow from the body. In other cases they are there to counteract lift at the rear end which can make a car oversteer at high speed. The Audi TT comes to mind. When it first came out there was no spoiler, and owners were swapping ends at high speed - not good if you want repeat customers. So subsequent models have a rear spoiler to maintain neutral balance at speed.

Same with front spoilers, they don’t generate downforce so much as the prevent lift. I’ve driven a few cars without front spoilers, that, due to there front end styling, generated a fair amount of front end lift at high speed. Very unnerving. In summary, spoilers don’t generate downforce so much as prevent aerodynamic lift.

Wings, on the other hand, like on the Daytona and Superbird make downforce. Like an airplane wing turned upside down, they are designed to create downforce with minimal drag. They are usually found on race cars, few production models have true wings, they have to be fairly large to have much effect.

And finally there’s ground effects that Rogue Leader refers to. In the late 60’s Colin Chapman was the first to utilize the idea of a smooth bottom car with a couple venturi tunnels. The venturi tunnels created a low pressure zone beneath the car, in effect, sucking it to the road with no increase in drag.
Giff

 

thats great ! thanks a lot