In a math talk, is it better to display the number of slides left? In a math talk (at a seminar or a conference, not teaching) that uses projected slides, is it better to display the number of slides left or not? What are the pros and cons? Some people tell me they like it, others prefer when it doesn't appear. I'd like to have some objective comments about this.

For some context, talks in math are typically one hour long, so the number of slides can be large. I like to cut talks into a few short sections. Right now I'm using the following layout, displayed at the top of every slide (from the "Frankfurt" beamer theme):



The current slide in the current section is highlighted, as well as the title of the current section.
Halmos advises that in preparing a talk you should have a block of material that you can omit if you are running short of time.  But if the slides show number of pages left, you cannot do that invisibly.  For example: in an hour lecture, if you are 5 minutes from the end of the hour, but your numbering shows you are only halfway through your slides, the audience will be getting restless.