What would types be good for? There's all those "message-not-understood" (and so on), but there is also fancier stuff like Session types for channels, or regexp-like types for semistructured data.
Castagna provides an account on overloading in the publication that came out of his thesis, titled
"Object-Oriented Programming: A Unified Foundation". The thing with overloading is that it might give a more precise type to pattern matching statements, an idea that haunts me since ages.