It will help you to plan presentations which meet the main needs of your listeners. The second thing to bear in mind is that, while you are talking, the listeners are doing the real job. It's not the talking that counts, it is what remains in the minds of the audience when the session is finished. Your task is to help them do their job properly. Accordingly, you should try to organise your speech in such a way that it makes it impossible for them not to listen attentively.
Attention varies Normally a person listens with great attention at the beginning of a speech.
That is because he or she is there to listen, and they want the situation to be as rewarding as possible. Of course there are exceptions to this, but that is normally how it works. The initial concentration, however, soon drops to a fairly low level, but at the end of the session it rises again. Instead we may ask questions about how long this initial period of concentration is. We may even want to know how much time we have to deliver the information before the listeners lose concentration or fall asleep.