Joe Chiccarelli demonstrates a room mic technique borrowed from classic studio practice: pitch-shifting the room channel slightly downward to make a smaller room sound bigger and longer. The effect works because shifting pitch alters the attack and decay characteristics of the room sound, not just its tone.
In this case, tuning the room mics down just a few cents helped the snare sit better in the mix, bringing it forward without adding more level or competing with other instruments. It's a subtle move with a clear result.