Animations contribute to a more dynamic feel for the user so he or she stays engaged. In real life, movement hardly ever follows a linear function because there are a lot of external and internal factors that distort it. This is where other types of more complex interpolations come into scene, generating smooth effects, closer to reality.
It is not strange if this sounds familiar to you as we talked about animations. We talked about animations, interpolations, and so on in Chapter 8, User Interfaces with Scene2D. The difference between this and what you are about to learn is implicitly included in the definition that the author himself, Aurelien Ribon, gives for the Universal Tween Engine library: