The L bracket hooks over the peak, the 550 hooks to it, you adjust the 550 it to stabilize your foot. Gives you a stable position to shoot from. On any thing under a 5/12 pitch you normally will not need it but depending roofing material, but a 6/12 or better you'll need it. Seen many who thought they did not need anything until recoil happened. Another thing you might consider is 550 cord around the scope or in your pocket, for both hands climbing an pulling the stick up.