"The actual benefit ... where the downforce of the car ... because the car sticks to the ground so hard."
Could anyone who understands the technology expand on that and explain it in simple terms for non-experts?
But...those create drag, so there's diminishing returns in using them. Another option is to disrupt or remove the air flowing under the car. This can be done by passive airflow redirection using an undercarriage tray, or actively via fans/blowers, or both.
F1 designer Gordon Murray famously developed a racecar using a fan duct (the '78 Brabham BT46) which did so well it was immediately banned. He later went on to do the McLaren F1 road car, as well as various recent GMA sports cars with this feature.
Is this only a big Ad with a very far connection to reality?
For 99% of drivers, serious active aerodynamic features are irrelevant. You'll never be driving fast enough for it make a difference.
For racers, it's a big deal.
The debris that would get thrown out the back going down the road would be a serious hazard.
The actual concept is to reduce the pressure under the car to create downforce along the underside of the car (often ducted and pass through a rear diffuser for more efficiency.
The purpose of this is cornering speed. Rubber wheels have limited grip to translate lateral forces and avoid skidding or understeer, so downforce is used to provide a momentary vertical load to keep the wheel pressed into the ground to avoid slip.
We can easily generate downforce to go around corners, but it comes at a cost of adding drag, so straightline high speed is reduced. and the car is less efficient.
underside aero does not incur nearly as much drag penalty so is attactive on F1 and other race cars.
https://en.wikipedia.org/wiki/Brabham_BT46
"The "B" variant of the car, also known as the "fan car", was introduced at the 1978 Swedish Grand Prix as a counter to the dominant ground effect Lotus 79. The BT46B generated an immense amount of downforce utilizing a fan, claimed to be for increased cooling, but which also extracted air from beneath the car."