The only thing I can see thathas not been mentioned is that a lot of mechanicals open up with the blades near or close to 90 degrees out. Fixed blades have a much steeper angle back. I have heard people compare the two by saying the mechanical "chops its way through" while the fixed blade "slices through". I like to picture this like pushing straight down on a loft of bread. The bread gets mashed down until the blade cuts through. An artery wouldn't bleed as well cut like this compared to the slicing action of a fixed blade. This "chopping" action also makes the blade loss energy which results in fewer pass throughs. I was told to use fixed blades except on turkeys where you want the arrow to stay in the bird. That way the bird will fight with the arrow and not run off or fly away.

This is just what I hear but it makes good sence to me. I am not even on the same planet as the experts in the field.