According to Michael Wolfe in “Conclude with the conclusions”, a letter to the editor on pages 6-7 of CACM, 53(11), Nov. 2010
[…] “Presenting Your Project” […] made several debatable points about presentations, one of which was inexcusable: “…I always end with a Questions slide.”
You have just given a 25-minute technical presentation […] Your penultimate slide summarizes the whole presentation, including its “takeaway” message—everything you want your listeners to remember. Now you expect to spend four or five minutes answering questions. The slide you show as you answer will be on screen two or three times longer than any other slide.
So why remove the most useful slide in the whole presentation—the summary—and replace it with a content-free alternative showing perhaps a word or two? […]
My advice: Remove the “Thank You” and “Questions” slides, and leave up your “Conclusions” and “Summary” as long as possible.