Animation can exist within all components of an app and at all scales, from finely detailed icons to key transitions and actions. All elements work together to construct a seamless experience and a beautiful, functional app.
The most basic use of animation is in transitions, but an app can truly delight a user when animation is used in ways beyond the obvious. A menu icon that becomes an arrow or playback controls that seamlessly change from one to the other serve dual functions: to inform the user and to imbue your app with a moment of wonder and a sense of superb craftsmanship. Users do notice such small details.