Simply takes away any need to "shim" the mount, rings or scope. And some barrels are not perfectly parallel with the receiver. So you can place your scope/red dot on the mount, bore sight for elevation as you tighten the screws, and that can leave you almost "all" of the scopes ability to fine tune on the bench. The slots could be slightly longer than necessary, and design change could be made, but we've yet to see one move up or down just because of the slot.
Still have to use a considerable amount of the scopes left/right movement range oftentimes, but it never seems to be past a scopes ability.
Never expected manufacturers or Armory refurbs had serious concerns about the receiver and barrel aligning perfectly for sighting, as both sights are on the barrel. Seems to vary by country of origin also, and this mount is meant to "fit 'em all."
HAPPY 4TH OF JULY TO ALL!!!!