After I finished my "industrial year" at university, we were all asked to give a short presentation on what we had done "in industry".

Returning to university after my industrial year, I took a very dim view of the academic environment and resented being asked to do this task that was worth no credit towards my degree.

So I didn't rehearse or even make any slides, I just stood up and talked about what I had been up to.

And although I was by any measure an extremely inexperienced speaker, it was the best talk I had ever given. It was the first time I stood in front of a room of people and felt present in the environment while giving my talk, rather than monotonously reciting the rehearsed material.

So obviously different people have different experiences, but I learnt that day that rehearsing your talk isn't always helpful.

It helped that I really enjoyed my industrial year and had loads of interesting stuff to talk about. So maybe the more important thing is to be interested in the topic.