Honestly, I can't tell that much of a difference because I'm not that good of a shot!
However, Gale McMillian once wrote a very persuasive post to rec.guns about how lapping cures any imperfection in the rings' alignment with each other - i.e., the bottom rings are not always in a straight line. If a scope is seated in mis-aligned rings, the lenses are pulled off-center when the rings are tightened.
After reading this, I checked all my scope rings using the lapping kit from Sinclair International. I was surprised to find that every single pair of commericial rings was not true. The only rings that didn't need work were a pair of custom rings from MGW. Since then, I just lap rings as part of the normal process of building up a new rifle.
Regards,
Ken Strayhorn
Hillsborough NC
