Too little or too much pitch causes an uneven distribution of the linear force of recoil. If the pitch is off you will experience felt recoil more at the top or bottom of the pad than if the surface of the pad was more evenly distributed on the shoulder. Also, with improper pitch, the recoil can cause a pivot effect on your shoulder when the shell goes off so that the stock rises into the cheek increasing your felt recoil on your face and putting your gun out of position for a quick second shot.
Lastly, inproper pitch promotes improper gunmount, which will affect where your shot pattern goes.
FWIW
Hack
