As part of my roles as a PhD student, thesis supervisor and post-doc, I have literally listened to more than five hundred presentations. Unfortunately, many were very bad, making them an uncomfortable experience for both the presenter and the audience.
Over the years, I have made it a habit of asking speakers (both of good and bad presentations) whether they did a presentation rehearsal. Almost all good ones did. Without exceptions, all bad ones did not. From my experience, preparation in general and rehearsal in particular, are the most important factors influencing thesis presentation quality.
Intriguingly, this observation holds independent of whether the content is from a Bachelor’s, Master’s or PhD thesis. Rehearsal thus matters more than previous presentation experience.
This observation has been made by many others before me . Then why have many, if not most of the presentations I have attended obviously not been rehearsed?
Because rehearsing is boring, awkward and uncomfortable.
To be honest, the rehearsal is the part I like least about creating a presentation. It feels awkward to speak to an empty room. Will anybody enter at random? What will they think, seeing me standing there talking to myself with slides? Furthermore, rehearsal reveals flaws. It is simply unpleasant to discover new flaws in one’s work, especially if you regarded it as finished.
Finally, rehearsal feels unproductive. Especially self-rehearsal. Wouldn’t it be more efficient to directly rehearse with a test audience?
No. Skipping self-rehearsal is less productive, because your test audience can only give you a certain amount of feedback per session. Test audiences often feel that you can only take so much criticism at a time—even constructive criticism. They remain silent about all further problems. Furthermore, a bug can hide other bugs. A test audience might not understand certain parts of a presentation sufficiently to point out all problems. Only after the first set of bugs is fixed can the remaining ones be revealed.
In such cases, the test presentation has to be repeated to build confidence that most bugs have been fixed. Skipping self-rehearsal typically makes a repeated audience rehearsal necessary. Since they are harder to set up and take more time (every audience member wants to be heard), skipping self-rehearsal is a poor strategy.
It is also disrespectful. Test audience time is precious. They do you a favor. Return it by coming well prepared.
Rehearsing a presentation has a significant advantage, however. In addition to help fix your presentation bugs, it builds confidence.
You are much less nervous about a presentation you have rehearsed successfully. You know that you will be on time, that you have sensible slide transitions, and so on. If you have rehearsed it in front of a test audience, they have probably even told you that they liked it. Your next audience likely will, too. This substantially reduces nervousness before your final presentation.
 For example, in Persuasive Presentations, Nancy Duarte covers rehearsal in a separate chapter that precedes all other content on presentation delivery.