Non verbal communication is a very significant aspect of Public speaking. Consider these small examples. Someone you are talking with is saying "Yes", yet their head is shaking from side to side in a manner commonly associated as a "No". Or, a person telling you how happy (or sad) they are, yet they have a deadpan look on their face.
Like most people, when you perceive these incongruencies your inner dialogue starts questioning this as "Really?". You become confused as to what the person is really trying to convey. Much of this happens on a subconscious level, however the conscious reactions tend to take the same forms.
Depending on your type of personality, you are apt to respond in one of two ways:
You may try to find a way to remove yourself from the conversation,
You may like to stick around and try to figure it out as a puzzle.
Again, both these responses arise from the confusion between the words and the non verbal communication.
As a public speaker however, you don't want to illicit either of those responses from your audience. Having half the audience wanting to leave because they don't want to be there, and the other half only wanting to stay so they can figure you out, leaves nobody left who actually wants to hear your message.
The use of pauses straddles both these territories. Either when it's implemented to allow the audience to catch up with you, or a different instance when the pause is used to ignite a deeper emotional response.
There are many techniques which will help you develop your non verbal communication skill set. Understand its importance and use it to your advantage.
Commit to your success.