Pauses are both powerful and necessary.
They’re powerful because they show strength on the part of the speaker—the speaker has the confidence to let her words stand for a length of time rather than compulsively filling in those moments with sounds.
They’re necessary simply because the listener needs time to hear what’s been said, respond to it and file it away under either “hogwash” or “genius.”
Beyond that, there’s an implicit courtesy in a pause. A pause indicates that the speaker cares about that audience’s response. A pause implies—indeed, initiates—a conversation.
Great speakers include the audience in the speech by pausing to show that they’re relying on the feedback loop that audiences offer and that they care about how the audience is reacting.
I once watched a famous speaker give a speech in a manner that completely failed to involve the audience.