This is a technique this you come up with, when you are self diagnosing problems in your shooting. I know, because I've seen me do it. I use to do this very thing. I found that my follow up shoots were slow, because it made my front sight track off to the right. I didn't even notice it till a much more experienced shooter pointed it out to me. By relaxing my thumb, that allowed to front sight to track vertically bringing the gun back on target faster.