If you're going to do a film clip - something that is not interactive - then by all means prepare and rehearse.
If you're going to present to a live audience - and want to do something more than just "parrot off" a rehearsed speach - and modify your talk based on your perceived reactions from the audience - then certainly prepare, but don't rehease.
If you want to stick to the script - do a video.
If you want to present to an audience, and feed and thrive off their energy and feedback, then present naked.
Has it been worth your audience's time turning up - or should they have just downloaded the video......
