I use the small one.
I think it depends upon the archer. It takes me out of my "zone" and I'll probably remove it.
The issue is that I shoot a sliding pin sight. As you slide your pin, then you have to change anchor slightly. This changes the position of the nose button on your nose, defeating the purpose and making you feel like you are screwing up. The only thing it helps with is my degree of extension. If it is on the side of my nose too much, I know I need to expand my chest because I am short drawing the bow (it as at the wall, but my arm is not as straight as usual and so my draw arm is slightly back, this causes left right shift of POI for me).