Talks initially can be nerve wrecking. Some people say they'd rather die than do public speaking. I have given many talks all over the world. Initially at conferences to present a paper and later to give invited talks or keynote talks. Invited talks are great as you can present controversial and unpolished ideas or give a high level overview of your research. Usually, research follows this three step process: do the work, publish and present. I find that it is much better to present before you publish. You can find out what is unclear from your audience's feedback. My book on Fluid Dynamics for example is based on many talks that I have given on that topic. Talks are also a great way to visit many countries and meet many people face to face.

I hate practicing my talks. But it is crucial.