Animations and effects are important elements/aspects of modern mobile apps. Each app has dozens of similar apps available in the stores/gallery; you need to make yours stand out so customers will download yours. Beautiful animated UI helps it stand out.
Moving UIView from one point to another, (e.g., when the keyboard appears/disappears)
Animating properties like color or transparency
Parallax effect with UIScrollView, UITableView, or UICollectionView