Enumerating and testing for type equality each derived classes in one place (i.e. manual type switch) is certainly a bad code practice in OO languages. Yes, the better way is to let virtual method dispatch mechanism decide.
Depends. It's useful when you want to have all dispatch code in one place (as opposed to it being scattered across numerous files). Doubly so if your language (like most languages) lacks multimethods. Triply so, if you need to dispatch on built-in types you can't extend, which sometimes happens in e.g. Java.
