Stabilizing weapon for a prone shot.
When shooting sling prone, I do find it more comfortable to be off at an angle.
The key then becomes keeping everything consistent.
With a bipod and a rear squeeze bag, I need to be straight behind the gun.
If I get angled, the gun will jump off target whichever way I am angled and I have a harder time spotting my own impacts.
When I am square, the gun jumps right back on target before the bullet lands there.