Knapped heads are very sharp and have been effective over the last 5,000 years or so. As to what edge causes more damage/ less clotting, I don't know, I'm not a doctor (I know it's a big shock to everyone[8D]). The fact remains, a sharper head will penetrate deeper since it has less resistance than a dull head.

If you sneak a dull broadhead into the lungs, heart, or liver, the punture wound probably will be fatal, but as to what gives you a better "edge" in the field, no question, a razor sharp broadhead is where it's at.