When to use a slide.
"D" represents a slide's Disconnection cost - the loss in connection between listener and speaker when the listener is looking at the slide instead of the speaker. "A" represents the slide's visual Aid value – the comprehension or retention gained from the slide by the listener.
"D" is a negative value that is always there and grows with the complexity of the slide, among other things. The mainstream presentation paradigm fails to factor this in.
"A" is a positive value. The mainstream paradigm gives this value too much weight (it even assumes slides are what makes a presentation a presentation).
My point is that slides shouldn't be an assumption and that the speaker – their facial expressions, their hand gestures, their body movement – has a lot of visual value.
Think twice before using slides. Or only display a visual when you know it is very valuable and display a black slide the rest of time.