After more than 10 years of daily blog posts, they deserve a mention.
Some presentation templates have page numbers prominently featuring on every page. Page numbers are useful for coordinating viewers who each have a copy of a document in front of them: attendees of an investment bank roadshow with a pitch book in their lap, or people trying to pay attention on a conference call without a screen sharing tool. But in most cases, the presenter controls the slides and there is actually no need for them at all.
As a compromise, I tend to put them really, really, tiny in the top right corner of a slide in a faded font color. You don’t see them if you are not looking for them.