The NASCAR guys are the absolute best. I've seen them there as the car is still moving (ok, in NASCAR the cars tend to slide a bit in the grass, but still).
I think NASCAR expects many spins, shunts and pile ups at every race, they must have multiple crews as a dozen or more cars will be involved in one collision, sometimes several times each race. Without enough crews how would they decide who is most in need of rescue first.
Thankfully multi car pile ups are extremely rare in F1 these days. I'm sure there are back up crews amongst the F1 track marshalls when all the designated rescue & medical squad is deployed, I don't think NASCAR has track marshalls in the same way as FIA sanctioned races.