Of course, at the intellectual level we usually understand how a speaker's performance is influenced by the attention and responsibility they have when addressing an audience. Nonetheless, we will still feel uneasy and are unlikely to trust a nervous presenter.
In short: if someone is nervous, it’s hard to buy what they are selling. It is much easier to buy from someone who appears self-confident.
If you yourself are not comfortable, you can’t make your audience feel comfortable either. You and only you are the most important visual that there is in your presentation. So don’t confuse your audience. If you aren’t comfortable while presenting, you need to learn how to make yourself feel comfortable.
-jk-