One of Disney's 12 principles: good staging leaves no doubt about what the viewer should be looking at right now. The test is whether the silhouette alone reads clearly, whether the camera (or screen) frames the important thing, and whether competing actions aren't stealing attention from each other.
In UI this becomes "animate one thing at a time." If five elements pulse, bounce and recolor at once, nothing actually gets noticed. Staging means brightening and enlarging the one thing you want seen while dimming or freezing everything else to create contrast.
The left panel below has no staging — four identical shapes pulse at the same size and speed, so nothing stands out. The right panel uses the same setup, but the background is dimmed and static while one shape glows and grows — the eye goes there automatically.
When to use
Reserve it for the one state change the user must not miss — an error banner, a completion toast. Animating the whole page at once defeats staging entirely.