Not needed for sure, but I like to take the extra steps to get rid of the “what if’s”. My rule of thumb for lapping scope rings anymore, is if I use inexpensive rings I’ll make the effort to lap them for sure. I was truly impressed with how concentric these FX no limit rings were. Just the other day I bought a set of $20 rings that came in a flat dark earth color, to match up to my Hercules Bully that already had a scope and matching stock that same color. I threw on the concentric pointers first, and they were off like a strong 1/16” from being in sync with each other, so those rings got lapped.
As as far as not ensuring the vertical cross hair is not dead center with the centerline of your bore, what’ll happen is when you take longer distance shots you’ll see drift either right or left, say, instead of vertical drop(expected) directly below your point of aim. That means your cross hairs could be tilted ever so slightly that you can’t really tell by looking thru the scope, but the problem is there.
Another method explained to me thru this great forum, is the mirror method. No fancy tools needed. Just brace your rifle nice and snug on some type of rest, set your scope to its lowest magnification, parallax set at about 10 yards, and look thru your scope into a mirror at about 10 yards away. Rotate the scope so the vertical cross hair indexes perfectly over the center of your bore, and lock it down.
To check against canting, I use either a plumb bob hanging on a long string, or my garage wall cross hairs. The plumb bob works well but not good at all on windy days.
I took my 4’ level and drew pencil lines 3’ tall and 3’ wide, making a cross hair on the garage wall, then lay one side of blue masking tape directly against the pencil lines. I actually use that more for checking and setting my wheeler scope mount anti can’t level.
