CEE uses that on his 16" chuck. That means for that 5inch-ish range of tubes and barstock he is clamping on, all or all but one of the teeth engage the scroll. These jaws are almost 2" thick, so say, 2" X 11 teeth X 3 jaws, with a .100 advance on 1 turn (these measures are approximate from the vids). Thus he has about a 25:1 advantage, so 200 ft lbs results in 5000 lbs of force available. Worm gears are about 70% efficient, so that leaves 3500 lbs of force distributed over 33 teeth/scroll section. About a third of each tooth will be holding the majority of the force, so, say 66 inches / 3 or 22 inches, or about 160 lbs per tooth. at 1/8 inch depth of scroll this isn't damaging in any way.
It looks scary and bad, but it is fine. I was freaked out when I first saw it, but I ran the numbers, so I'm not worried.
However, using a cheater on a small chuck with 5 teeth engaged over a 1 inch jaw this force would wreck the scroll or the teeth on the jaws.