There is an advantage of using the sight ring vs centering the pin with multi-pin sights...I've done both, both will work, currently use the sight ring...
The advantage is consistency, same anchor point, same bow arm position and bending at the waist to put the pin on target...If you think about it, there is no way to place your top pin in the center then the bottom pin in the center without changing your anchor point or your bow arm position....
I've never had an issue with centering my pins. I don't change my anchor point, either. I never saw the need to add another step of lining up a sight housing when it wasn't needed.