I usually stay within the logical boundaries of grains to weight. We always went by 8 to 10 grains per pound for hunting arrows; maybe lighter for field and target, depending on what we were shooting at the time.
I choose the arrow best suited to my bow and me, then maximize flight and performance characteristics so when it does hit, all the power is delived on the tip of the broadhead.
Basically, it's up to the individual archer, whether or not you want 8 or 18 grains per pound.
The bottom line is that it needs to fly perfectly off the bow and hit the right spot to be of good benefit.