Motion as explanation, not decoration.

Motion with a job

Most interface animation is garnish. The useful kind answers a question the user is already asking: where did this come from, where did it go, what just changed. When a card expands into a detail page instead of cutting to a new screen, the motion is doing the explaining — remove it and the page stops making sense on its own.

The test is simple: if you can delete an animation and lose nothing but polish, it was decoration. If deleting it makes the interface harder to follow, it was load-bearing. Keep the second kind, cut the first.