I often get the complaint that refining a presentation takes scientists away from their research for the sake of marketing. This represents a fundamental misunderstanding of what can be achieved through careful preparation of a presentation. First an example...
Recently a graduate student invited me to his PhD oral exams. The exam consists of a 20 minute presentation followed by questions from the committee. I asked the student if he would like me to review his presentation prior to the exam. He replied that the presentation was not ready, and as it turned out, he worked on it right up to the exam. The presentation itself was adequate (given the low standards for many biomedical research presentations), but the question and answer session did not go well.
It was obvious that had the student reviewed the presentation with an editor prior to the oral exam, and had that editor not been an expert in the student's area, and had that editor insisted that every slides have meaning, many of the questions would have been anticipated. A detailed slide-by-slide review by an objective outsider is the best way to gain an understanding of one's own material. It forces the scientist to think about issues in ways they have not considered.
But the lessons go well beyond a thesis exam. Biomedical research is very much a bottom-up activity, with little theory to structure research or suggest obvious ways to organize research results. A presentation is very much a top-down activity, defining the major ideas and then bringing in supporting data to "prove" those ideas. Presentation preparation is one of the few activities that forces the biomedical researcher to organize findings in a highly structured way. It forces the researcher to relate findings to scientists in different but related disciplines. It is a necessary follow-on for the detailed lab work that often leaves scientists thinking that laboratory technique, rather than scientific ideas, are the end points to research.