Osmiu's comment is relevant. Barbed arrows, especially those with pointy barbs, fulfil Stephen's purpose better than loosely attached ones. An added advantage in military situations is that trying to remove barbed arrows would make things worse.
Not all barbed arrowheads have functional barbs though. I would argue the barbed shape of the large English "bearded" arrowheads is designed to save weight on an already overweight head. In this case the barbs served to increase the cutting surface with less overall mass.
Getting back to another part of the argument, what about loosely fitted arrowheads? Khoi hunters use loosely fitted foreshafts to deliver poisoned arrowheads to large game in southern Africa. They also use weak bows to shoot the arrows because their poison is effective enough not to need deep penetration. War bows shooting heavy arrows require a firmly attached head otherwise the slightest deviation to a perpendicular impact will cause the shaft to hinge at the tang and either shatter or waste most of the arrow's energy before penetration.
The standard weight ratio in the Middle East for war arrows was for the head to weigh 1/7th of the head plus the shaft. Therefore the shaft was six times heavier than the arrowhead and there was a strong tendency for breakage unless the arrowhead was firmly attached. In extreme cases where the arrowhead was meant to penetrate hard objects, the tang length was increased.