Imagine you have archers in a stealth forest, but you want to let the enemy cavalry pass because you want to use the archers against some other group. Without No Attack Stance, the archers will fire upon the cavalry, giving away their position and making the ambush impossible.
Also please make Stand Ground behave like the other formation buttons. It is super weird that it stops the marching, and even weirder that it disables itself if you move the units.