If a picture is worth a thousand words, an animation is worth a thousand pictures. Motion design is the "Secret Sauce" that turns a good website into a great one.
Functional vs. Decorative Motion
Most designers use motion because it looks cool. But the best designers use motion to provide Context. It shows the user where an object came from, where it’s going, and what its relationship is to other objects on the screen. It’s about building a mental map for the user.