It wins you more code reusability with less code written to accomplish aforementioned reusability.

I always run into silly inheritance chains, type coercion or adapter fns/methods to handle reusing code for unlike-types, rather than relying on a common base of functionality regardless of where it was derived from (function API, inheritance, mixin, etc).

Best way I've seen this done is in Clojure. Good mix of the best of both worlds in terms of static and dynamic typing, multimethods, protocols, essentially structurally typed arguments, etc.