Animation that never stops moving reads as busy and hard to follow. Animators deliberately freeze a key pose or expression for several full frames, giving the audience's eye time to catch up and register what just happened — comic timing is, in large part, built on holds.
In UI, a hold is the brief pause right after a state change. When a toggle flips or a save completes, staying put for a couple hundred milliseconds before moving on again stamps the change into the user's memory instead of blurring past it.
The top lane below never holds — it swings back and forth continuously, and it's hard to tell what deserves attention. The bottom lane clearly stops at both ends of its swing, and a ring flashes around it while it's held, marking "this is deliberately paused."
When to use
Use it to confirm a change the user just triggered — a save, a toggle flip. Keep it short, roughly 200–500ms — hold too long and the UI starts to feel unresponsive.