Prezi is lacking one feature… a feature that would allow “slide decks” to be shared after the presentation, with references to specific slides.
Someone just shared a Prezi “deck” with me, wanting to discuss a particular section. In the absence of slide numbers, she was unable to pinpoint the section to discuss.
Furthermore, some people are in academic and scientific environments that REQUIRE slide numbers. They’ve been posting to a thread on the Prezi community forum for a couple of years, and there’s been no change in the product… I think because slide numbers offends the aesthetics of the developers.
Other people will tell you to put slide numbers on any deck, as it detracts from the cinematic experience of the presentation. I will tell you to make it usable first.