Depending on the wood you use and the length of the footing, the footing doesn't add much physical weight. In my experience with a 11/32 POC shafts, about 25-30 grains with a standard 4-point hardwood foot about 7 inches long. The difference in weight is only the difference between the weight of the hardwood foot and the POC, not the entire weight of the hardwood foot, because if it weren't there, the space/length would be occupied by the POC shaft.
It does slightly increase the static spine a pound or three, but given the slightly heavier front end, not enough to worry about in terms of affect on arrow flight.