It is confusing to start with,but you can understand it.The acceptable range for f.o.c. is 7-15%.With 9-10% being goal.What that means is that the arrow is 7-15% heavier towards the front of the shaft.You have to have the front of the arrow heavier or it would fly backwards.Just like throwing knives.Any way you release it the heavy part hit's first(on tuned knives anyways).If the front is too light the end of it will try to come around to the front.You will see it as unstable flight as the arrow "flips" "kicks out",or makes circles.What is happening is the front isn't heavy enough to maintain stable flight,and as the back end is trying to come around the fletchings are fighting to keep the arrow stable.That's another reason why it is more evident with broadheads rather than field tips.The larger a broadhead is the more wind resistance it makes,and therefore makes a harder job for the fletchings to maintain proper flight.When you have unstable flight like that the arrow loses speed,and when it hits the target in all likely hood it will be trying to come atan angle as the arrow enters awkwardly.Instead of hitting straight on,and transfering the energy to the target it will be losing energy trying to maintain flight.Like trying to hit a cue ball as hard as you can,from a bad angle instead of straight on.

If an arrow has too high of an f.o.c. it will drop sooner.All things being perfectly equal you can actually gain yardage from a properly balanced arrow,because flight is stable,and it isn't like sticking a piece of bubble gum on the end of a straw(too high% f.o.c.).It will shoot flatter.That will help your pin spread.But in a way it is better to have a higher % f.o.c. than too light of one.You'll just have to use more pins..I prefer to have mine balanced,rather than front heavy.Most people here seem to prefer front heavy arrows.If I'm wrong I'm sure someone will correct me.