PowerPoint isn't content to sit in the background and project the occasional chart, graph or bullet list. It wants to organize the talk, to manage the presentation. There's always going to be a slide up, whether you need it there or not.
S. Bryant, A. Forte, and A. Bruckman. GROUP '05: Proceedings of the 2005 international ACM SIGGROUP conference on Supporting group work, page 1--10. New York, NY, USA, ACM Press, (2005)