They do not cover any damage to your car, if any damage occurs they will deny all responsibility and make you sign a waiver at the drop off.
I parked a c class once with purple parking and it came back scratched, I never got a penny for the remedial work.
When I was on the plane I could see how they parked my car and I can only think they climbed out through the window, there was no way they could have got the door open.
Since I have heard all sorts of stories of spotty teenagers racing cars around the compound.. Never Again... Pay and display every time.