Bigger pellets leave fewer holes than smaller pellets. At the ranges I tend to shoot birds, smaller shot makes more sense, as they have plenty of energy up close and are more numerous, increasing the chances of vital hits and, per above, they shoot patterns that open quickly. But, that also means there's more chance of biting into a smaller pellet when you eat the bird. Not only are there fewer big pellets in a given weight of shot, and therefore fewer of them in the birds I shoot, those big pellets will penetrate deeper, so there's less chance of finding them in the meat. This is why, although I believe No. 2s are great goose pellets, I shoot BBs at them, and why I often shoot No. 2 at teal, even though No. 5 and No. 6 make more sense.