Probably next to none but that's why it's nice to have an accurate rifle to begin with. If the best you can hold is 2 to 3 MOA from a non supported position and you have a 2-3 MOA rifle to begin with then you may or may not hit the pie plate.Since so many spec'd <1MOA requirement on their hunting rifle, I wonder how many can realize it firing off hand, or slinged up, or leaning against the tree.
Shooting in competitions we shoot in all kind of messed up positions and its under time. It's built a lot of confidence for taking shots on deer. I still wait for clean shots on them but I haven't let a moving coyote through the field in a while.