Actually there is, in the factory Crossfire manuals (not the owners manual) it states that fully deployed wing will exert 40 lbs. of down force at 80 MPH. While that doesn't sound like much, it should be just about right to stabilize the read of the car and add just enough pressure on the tires to keep good contact with the road. I'm sure the same holds true with the Panamera wing.

That wing looks like a typically well-engineered piece of Mercedes handy work and a fairly expensive piece to employee on a vehicle. Somehow, I don’t think they went to that much effort for marketing’s sake. But, then one would wonder why the SRT needs a large permanent wing, or the monster wing on that 911?