Audience members are usually waiting with anticipation about what they’re going to hear. Good presenters are people who carefully outline what the going to be talking about, before they begin. If they let an audience know what they’re going to be covering during a presentation, listeners are left in no doubt about how the session will unfold. Listeners know how the topic will be introduced, what key points will be discussed, and how the conversation will be wrapped up. This approach offers clarity that would otherwise be lacking.
If there are particular aspects of the topic more interesting to some audience members that others, they have time to mentally prepare for that section of the delivery. In any case following the progression of the unfolding conversation is definitely helped and illuminated by the summary suggested.