Never
My colleagues and I disagree about this. Some use clipart or photos to demonstrate the emotion or “mood” of a PowerPoint. Not me. Call me a puritan.
I tell my team to not include clip art or superfluous photos. It shows a lack of substance. If you need to cut/paste photos or something to “spice up” your presentation, it means that you don’t have anything to say and you are wasting people’s time.
Never
The following photos are from a presentation I saw today. Ewww, bad. trite.
Never