This would be especially useful in portrait orientation on the 12.9” iPad.
I replaced my old 10.5” device which had the Grades/Comments/Files bar across the bottom in portrait mode. I was quite surprised to find it taking up side space on the 12.9” device when I hoped to have the full screen space for reviewing and marking papers. Being able to shrink the right panel to the right edge would work just fine, maybe even better since my hand used to cause the bottom bar to jump open unintentionally. The right edge would keep it more out of the way.