I've had entirely too much wine to be treated solemnly, but I've read the replies and my contribution is that multifaceted characters are the most interesting. Even the most evil characters have a motivation, something that brings about a sympathetic response. I don't think a character drawn as wholly villainous or wholly virtuous is anything more than a caricature, and is responded to as such. As pointed out, throwaway characters have limited function, and they're not built for emotional response but merely to steer a concept. At times that can be a valid use, but I would hazard to say that in most cases it's not something a seasoned writer would use.