In a Zoomable User Interface (ZUI), you can move up and down the scale of a spatial dimension easily. This feels very natural when you’re zooming through something that you have some physical intuition about, like a picture of the inauguration, or a map of the planet. It can be very disorienting when you’re zooming through an abstract space.
Here’s an especially nice example of where it can work well: Cell Size and Scale.
It’s always eye-opening to see how tiny cells are, and then to see how tiny (most) bacteria are relative to eukaryotic cells. Consider: you couldn’t cram one of your chromosomes into an empty E. coli shell if you used a spatula and two shoehorns. I don’t know if I’m more impressed with my size or E. coli’s minuteness.