The principle
The more you say, the more common you appear and the less in control. Powerful people impress and intimidate by saying less.
The application
Silence forces others to fill the room — and what they fill it with reveals them. Short answers read as considered; long ones read as anxious. The instinct to explain is almost always serving you, not your listener.
The defensive tell — how to spot it being run on you
When a senior person sits quietly through your pitch and finally asks one short question, they are not slow. They are letting you do the work and pricing what they will concede. The pause is the negotiation.