Agreed, Jeff, but I think Bob O was speaking entirely of the subjective aspect of mastering - deciding to make something brighter just because you think it sounds better brighter, for example.
Personally, I operate in the mode that they are hiring me for my technical abilities as well as my subjective ones, so if I think it's better brighter, or darker, or whatever, I do it unless instructed otherwise. Part of what we do is subjective and more often than not (IMO) is the reason you are hired - people like your subjective decisions.