When using some designs of scope mounts, lapping is recommended to get the best performance. Lapping can increase the amount of surface contact between the ring and scope tube, and also help with proper alignment between the scope rings.

Do Leupold scope rings need lapping?

I've read Leupold new rings the ones with ridges inside the ring doesn't need lapping. Personally I've used Warren or Weaver two piece rings w/o issues but there are many good ring choices.

What does lapping rings mean?

To oversimplify, lapping simple means “sanding” the interior of the ring to obtain a perfectly smooth and precisely shaped surface. ... Using a perfectly shaped steel rod, one grinds and smooths the rings using a lapping compound until the rings are ground ever so slightly into the perfect shape.