Dubbing is inherently weak compared to the original vocal performance. You are definitely losing much of the power and nuance of a performance when it's entirely dubbed after the fact.
However, all of the dialogue in virtually all Italian films through at least the early nineties was dubbed, including the Italian dialogue. This is due to the fact that the standard practice in the Italian film industry was to not record any "on set" dialogue or sound. They did this for various reasons, but primarily because it was cheaper for them to do it this way, and also because they frequently used international actors who couldn't speak a word of Italian (these actors generally delivered their lines in their respective native languages). So with these films--and this includes every spaghetti western ever made--you don't get to experience a more genuine performance by listening to the Italian soundtrack and reading English (or whatever your native language might be) subtitles. This is not the case with films in general, certainly not American films, where the majority of the dialogue is recorded on set, and only scattered lines here and there have to be dubbed later because of extraneous noise on set or inaudibly/unclearly delivered lines.
