Easing controls how quickly an animation speeds up or slows down. It is like a bicycle starting gently, moving steadily, and then slowing as it reaches a stop.
A panel that opens can ease into place rather than moving at one stiff, constant speed. This small detail can make the action feel more natural and help people follow it.
Choose a simple motion that fits the action. Easing should not make a control feel slow or unpredictable, and it is only useful when there is movement to shape.