Animations may appear to just be a nice bit of polishing on top of your user interface, but they can also serve an important purpose. In any design, whether it's a building, an API, or a user interface, it's good to try and follow a principle of least surprise. Try and offer your user things that make sense without them having to try and understand the details of how it works. A good example of violating this principle is when a button is wired incorrectly. If you were to press the copy button on a printer, and instead of making a copy it printed a test page, this would be a surprise. You expected the machine to do one thing because of the label, but it did something unexpected.
It's always important to consider what your user will expect to happen when they look at or use your application's user interface. Using well-known names and icons for the elements of a user interface help make it instantly understood by your user, but sometimes your application will change what...