This helps spread the stress of the bend over the entire length of the bend, lessening the deformation of the cross-section. This also creates much more uniform stress throughout the bend, resulting in a stronger bend as well.
this is a key point.the deformation i showed in the picture above is very uniform from one end of the bend to the other-a cut across any part of the bend will have the same profile.as pointed out,this will not be the case with the HF bender,plus you will usually get dents in the topside from the rollers.also,the dies for the HF bender are sized for sch pipe,not tube sizes.all tools still have their uses,though-and neither of these are good for exhaust.i'm surprised no one with a tubeshark has piped in here.