Fiberglass batt insulation with a paper vapor barrier had installation instructions
printed on the paper. The paper was wider than the batt, maybe 1/2″ on each edge, and the installer was instructed to fasten this extra 1/2 “, not to the face of the framing member, but to the inside edge of the framing member. This held the batt away from the finish wall
creating an air space.
In the last few years I have seen the vapor barrier, particularly poly, fastened in one continuous sheet across the framing member edges, no gap.
Is the gap necessary or not.