LAST EDITED ON Oct-15-14 AT 08:53AM (MST)[p]An arrow needs to be weighted more to the front of its mid point than to the rear to maintain flight stability. Think darts thrown at a dartboard, as an extreme example. Darts are very heavy up front, and if calculated would have a very high FOC %. Arrows don't need it to that degree, but a certain amount up front is necessary. Typically you want the front half of your arrow to weigh 7-12% more than the back half of your arrow.
If you want to waste a few solid days, search FOC on archerytalk.com. Loads of reading there. Some say, to which I agree, a higher FOC helps with down range accuracy, and aids in penetration.
My arrow setup is just under 17% FOC.