Comment by bobbylarrybobby

Computer UIs need animations for the same reason they need shadows, gradients, and momentum: because these are aspects of the physical world that we already know how to interpert, so can be used "for free" to aid our understanding of the UI. Not using animations would likely be more taxing on our visual processing because nothing in the world moves discontinuously, so that would be a new thing to learn when using a computer. The primary reasons not to use an animation should be technical: you can't have it run in a short enough time and still look good, not drop frames, conserve battery life, etc.