Gesticulation has long been a part of public speaker training.

It helps frame your words and your message and also direct meaning in a way that punctuation does in the written word.

As punctuation is to reading, gesticulation is to speaking.

It’s part of body language being part of speaking to someone (a person or an audience) and can help people relate to the speaker.

That particular gesture was famously popularized/lampooned due to Bill Clinton