Often designers want bullet points or small blocks of text to appear as they are spoken in the narration, so you might want 5-10 short pieces of text appearing at different points on a slide. It's extremely common. I don't see a way to do that on a single slide since you're limited to one text element. THe only way would be for them to be stacked and have virtually 10 slides worth of material for the user to scroll down through as the narration progresses, requiring extremely active scrolling along with the narration - which will NEVER happen. This is very sloppy design and not very functional!