It's an old quote from Shakespeare: "Brevity is the soul of wit". Oral communication in today's world, which is nonstop unless you're fast asleep, requires capturing the listener's attention and then communicating quickly. Most people aren't used to listening for more than a few minutes at a time.
I won't argue whether that's good or bad, but when we hear of sermons that once lasted three hours and piano concerts that started with nine mazurkas as an introduction, we understand the difference between days of yore and today. People in the past looked forward to listening because there were intermittent periods of silence for balance. Unless you arrange for silence with great determination, you won't find it in today's world.
As communicators, then, we need to look at two things: the hook, which gets the audience's attention, and the substance, which presents what we want them to know. In both writing and speaking, the hook is more important nowadays than ever. Bombarded with competing messages, audiences learn to tune out most appeals, deciding very quickly whether they will invest in a person's message or go on to something more interesting.
Your hook must be immediate and engaging, especially if you're an unknown quantity. We're likely to give some leeway to Martha Grimes, despite the fact that she has trouble speaking, because we know she has valuable things to say. But if you come to hear a first-time author like me speak, I'd better say something good right away or I become just another salesperson hawking my wares.
It's important to keep the substantive part of a presentation succinct and on some sort of planned outline. Outstanding author Laura Lippman is also a master of speech planning. Each section of the talk I heard her give led logically into the next, and planning and practice were obvious. The hour she was allotted passed quickly, and when the time was up, she ended it pleasantly but firmly, offering to stay longer to speak with individuals who had more questions but giving the rest of us leave to go with her thanks for attending.
Sticking to a timetable, moving smoothly from topic to topic, and keeping the audience's interest in mind make a presentation interesting, but it requires practice. Successful people never "wing it" because that draws out a speech. As Pascal said, things often are long because we haven't taken the time to make them shorter.
For any speaker, the better the planning, the more to the point the speech will be. That focus makes the time fly by for the listeners. Oral communication done well makes the audience wish for more rather than wishing they'd brought along their Ipods.