Anticipating an action
In nature, most actions have a preceding movement. Be it a subtle eye or eyebrow movements to anticipate a head turn, or a full-body preparation for a jump.
Giving proper premise to your characters' actions will not only make them look more natural, but will also give visual clues to your audience so they know what's happening on the screen and where to look next. If you think of it like that, you may conclude that the anticipation principle is a storytelling resource in the animator's tool set.
As any other animation principle, you can use it (or remove it) for dramatic or comedic purposes. For instance, a character may leave the screen without anticipation, leaving only dust in its place and a proper sound to make the audience ...