The benefit of using an Hash as parameter is that you remove the dependency on the number and order of arguments.
In practice this means that you'll later have the flexibility to refactor/change your method without breaking the compatibility with the client code (and this is very good when building libraries because you can't actually change the client code).
(Sandy Metz's "Practical Object-Oriented Design in Ruby" is a great book if you're interested in software design in Ruby)
