From a New York Times Magazine article featuring Brad Bird ("The Incredibles"):
[Animation's] success depends on finding a physical expression that is recognizable yet beyond what occurs in real life.Fred Astaire had unusually large hands and learned how to use them in a way that made his dance more dynamic; he’d fold his hands for most of a routine, then flash them out for accents at key points. Their sudden increase in size made those moves pop in a way that other dancers couldn’t match. Animators use tricks like this all the time in ways that the audience never sees but always feels.
Check out this Astaire clip ("Putting on the Ritz") for a demonstration.