What happens if you export the animation?
What happens if you re-import the animation?
Can I temporarily disable or remove tracks?
Is there a way to see the difference of my edited animation versus its source?
Inside the Show menu options, you can enable the Source Animation and (or) Baked Animation for display in the viewport. The Source Animation can be seen as a white skeleton, while the Baked Animation can be seen as a blue skeleton as shown in the image below.
Just make sure that you have enabled the display of Bones from the Show -> Bone Hiearchy menu.
Can Animation Layer Editing be used to create root motion?
Yes. Select your Root Bone and key it, then scrub the timeline forward and move the Root Bone and re-key it.
Above we have enabled the Source and Baked Animation preview where the white skeleton is the source animation.