A spring animation imitates a flexible object moving and settling, like a spring that bounces a little before becoming still. It can make a screen movement feel soft rather than mechanical.
For example, a card may stretch slightly when pulled and return to its place when released. The effect can help show that the card responds to a person's touch.
Keep the bounce subtle and short. If an interface keeps wobbling after the action, it may distract people or suggest something is wrong. A spring effect is a style choice, not a requirement for every movement.