Camera Pivot doesn't do what you think it does.
I have no idea what this video is going on about, but it fails to highlight the difference in my opinion.

By default, using A or D in legacy mode will cause the camera to stay in the same location, but rotate to follow the character (causing he character to run around in circle). With camera pivot disabled, the camera will keep the same rotation, and instead move to follow the character (causing the character to run in a straight line, as if you were holding LMB).