If you have big fingers, they fill that area behind the trigger guard, protecting your middle finger. They also add a little extra diameter at the thinnest part of the grip, improving feel. I have used several on my snub's, and they work. My only issue is they do not lengthen the grip, leaving my ring finger on the bottom edge, and my pinkie hanging free - A poor grip for recoil control when firing fast double action. But that's more a problem with my particular hand size, and an issue on all J frames for me.
Larry