Footed shafts are a bit stronger, at least if one is footing cedar. Hardwoods, of course, don't need footings. They're strong enough on their own.
Footings add a little to the FOC, probably 3% or so depending on the length and diameter of the footing and the material used. Keep in mind that the footing replaces the wood that's already there, so the increase in weight/weight forward, is not the weight of the foot, but the weight of the foot minus the weight of the wood that was there originally. Putting a 6-inch or so hardwood foot on a 11/32 cedar arrow increases the weight/weight forward by about 30 grains, give or take a little.
That translates into about 3% FOC on a standard constructed arrow, i.e., intermediate length and point weight.
I might add that a 10-inch shaft taper on the nock end reduces the arrow weight by about 30 grains. So by tapering and footing a standard 11/32 shaft, you can gain 5-6% FOC. Adding 50 grains to your broadhead weight will do about the same thing.