If all you are given is a bunch of "cheap" shots that pattern very poorly, chances are you would instinctively load more shot in a shell to improve your odds of hitting a target. Quite plausibly, this natural instinct was what invented shot gun in the first place back in the olden days of hand cannons.
- Given the same amount of charge, the resulting thrust it generates will be distributed among the projectiles, including wad, buffering material, etc. according the the Law of Conservation of Energy. Therefore, the more stuff you pack in a shell, the less energy each pellet will ultimately carry when it hits the quarry.
- As with the fire-exit of a room, if you fill the room with people beyond its capacity, evacuation will be slowed. Even worst, stampede might occur in case of a fire. By the same token, if a shell is overloaded, the pellets will jam and interfere each other. Energy will therefore dissipate; and the shot pattern will be negatively affected.