The ribs serve the purpose of protecting; lungs, hearth and liver and more. The ribs articulate posteriorly with the thoracic vertebrae, and most attach anteriorly via their costal cartilages to the sternum , which makes it pretty stable.
When an area is stable, the movement capacity decreases. But the slight movement in the ribs are essential, because it’s necessary for being able to breathe. If one gets injuries around the ribs; which could be a locked(dysfunctioning) rib, bend or broken rib, it hits the breathing capability. And is usually very painful.
It’s also important to have proper breathing, that your ribs are functioning correctly and do not lock in.