Joe Mazzulla talks about margins more than my 9th grade English teacher. Much like Ms. Smith, Joe is worried about undue benefits from fudging the margins. In the case of the Celtics, they let Atlanta get away with fudging the margins in Games 3 through 6, and it almost led to a surprise Game 7.
By “margins,” Joe is really talking about valuing possession. The two biggest ways to lose the possession game? Give up offensive rebounds and lose the turnover battle. The Hawks destroyed the Celtics on the glass, which frankly might be underselling it, but the turnover battle was a push.