I'm especially curious about the last point - that screenshot slides are especially bad. I gave a presentation to an audience comprising my target market, and

I'm especially curious about the last point - that screenshot slides are especially bad. I gave a presentation to an audience comprising my target market, and did almost all screenshot slides - the purpose was to give a high-level tour of the app. I would rather have demoed the product in action, but it was an iPad app and the facility lacked the means to Airplay the screen. From what I could tell, the presentation went ok - people came to talk to me about the app and they were quite excited. So it worked out ok for me. But circling back to my question, given that experience, I'd like to know what the context is behind "screenshot slides are especially bad" - why? What should be done instead?