They call it "aftershocks" - that slightly too-long moment of reaction, in which time most shows would have cut away. Particularly for the female characters, the device is revealing and crucial. As Variety points out, even those interactions that would seem to exclude women give them a "voice" in these scenes - often the loudest one. These moments are carefully plotted: each episode is preceded by a "tone meeting," in which the editors plan the distinct feeling they're going for. And while "dead air" is normally anathema to television - and was initially deemed "too slow" by AMC - the silences are a big part of the show's power.
Take this moment: on the page, it might look like Don's in complete control, displaying his sophistication and shutting down Peggy's attempt at small talk. It's in the silence that we see Peggy decide it's not worth it, and take the situation back - and in Don's look at her departing back that we know he knows it, too, and that a power shift has occurred.
This scene - in which Joan's husband tells her he hasn't gotten a much-desired promotion - would be effective anyway. But it's the moment of silence, in which we see Joan drop her ever-present game face and admit defeat, that makes it devastating.
There are only three lines here, when you think about it: all the tension comes from the silences and the pauses - and it's really tense; you feel a physical relief when Grandpa Gene reveals that he's not going to yell at Sally for stealing his money - or even mention it. His look says: I know, I have the power, and I'm wielding it benevolently. It's over. And somehow it's more suspenseful than a procedural packed with corpses and nonstop dialogue.
'Mad Men' Cutters Cue Subtle Moments [Variety]