When hanging heavy moving heads, this type of clamp is an immense help. It is designed to accept the full weight of the instrument as soon as you hang it onto the bar or truss. This frees up your hands to finalize the position before tightening the thumbscrews to lock it in place. Similarly for tear-down, loosen the clamps, then use both hands to lift the instrument off the truss- no more fiddling with one hand on a stubborn flip-over clamp while supporting the entire weight of the instrument with your other hand.