When it comes down to it, the importance of public speaking is linked to every part of the event. The speaker, the audience, the topic, the speech, and the presentation.
When you step back and look at the larger scope, and the interconnectedness between these basic aspects, the importance of it becomes much more clear and, well, important.
First of all, the distinction to you as a speaker has to be understood fully. It gives you credibility and defines you as an expert. It enhances your self-confidence and puts you in a position of leadership. It allows you to make connections you may not be able to forge otherwise.
The emphasis with regard to the audience is having them feeling empowered in some way. Hearing your speech and coming away with information they did not know before, or a point of view they may not have considered without your presentation. This allows them to leave with a new knowledge, and that is powerful on its own. Multiply that by the number of people in the audience and the importance easily defines itself.
The topic is of huge significance also. The topic has got to be tailored specifically to your audience. Gender, age, lifestyle, hobbies, etc, all play a factor with regard to determining your topic. A speech about a more efficient way of knitting a scarf is not going to go over well with an audience of ATV enthusiasts.
The notability of the speech itself obviously is tied to the importance of public speaking. You don't want to bore your audience, and you don't want to be over the top either. You want the content to take them on a journey, to be relevant, and timely. You want to speak in the tone, manner and phrasing that your audience is accustomed to. Speaking to an audience of sports team coaches would require much different terms of phrase and vocal projection than speaking to an audience of wedding dress seamstresses.
The caliber of the presentation itself is just as much a concern as its content. Using the previous example, both audiences would be bored listening to a speaker who stands in one spot lecturing in a monotone voice. Though the content has to be different for both audiences, the presentation itself must be dynamic in its respective forum.
The importance of public speaking encompasses the whole presentation and everything within it. It is wise to devote the time and energy to your speech to cover all these facets to guarantee your success.