Footwork is the art of moving your feet to get into position. Footwork is important at all levels because when you are in good position, you are able to generate more power in your strokes and achieve higher consistency. If you are slow on your feet, a ball that comes too close to you will force you to return it awkwardly.
Ryu Seung Min is arguably the best on his feet and can move great distances in a short amount of time to load up a big forehand loop. Penholders are known for generally having better footwork since they often rely on their forehand more and prefer to step around
and use their forehand instead of staying put and using the backhand.
Footwork is often overlooked in developing players and developed later. Try developing it earlier!