Difference between Original and Root Node Position

Hi,

For Humanoid rigs, this different root motion options are explained pretty well here: https://docs.unity3d.com/Manual/RootMotion.html

However, I am working with a human rig that is Generic (for good reasons). But there isn't really any explanation as to how Unity calculates "Original" vs "Root Node Position" in animation import settings.

My model's root bone is at the hips, and I am guessing that for the Y position, selecting "Original" places the root motion of Y at the model's origin point. But I don't understand the difference when you select "Root Node Position" for the XZ translation and "Root Node Rotation" for rotation.

Surely, root motion is just root motion, the translation of the root bone, so how could this be any different between Original and Root Node Position options? I can see the transitions are better with the latter selected for XZ, but I can't discern what Unity is actually doing differently.