Rigify question: For 'limbs.super_limb', what exactly does Auto Align Hand/Foot do?

When setting the Rigify Type as limbs.super_limb I always set the Rotation Axis into manual because setting it to auto creates some weird rolls to the limbs when generating the rig. When set to manual the option to enable Auto Align Hand/Foot appears which I’m not sure what it does appears. What exactly does it do?