If you're flying a low inertia rotor (like the 22) then you should keep your hand close enough to get the collective down before you have time to say,..."what the fu,...!"
Flying the 22 myself I don't hold onto the collective for the entire flight. I don't rest my hand on my leg either, like in those videos (yeah I've seen them too) but I do rest it on the edge of my seat with my fingers lightly touching it,...or holding it up 'cause the damn thing keeps wanting to fall down!
Anyway, don't take too much stock in what you see on youtube, those pilots don't usually represent the best of us
