When Should a Consultant Question Decisions?

bay43270 asks: "Presumably, companies hire consultants because they need technical expertise. At some point (if not on a daily basis) a consultant is asked to do something that isn't in the best interest of the company (and therefore may not be in the best interest of the consultant in the long run). The consultant must ask 'do I just say "yes sir" and go to work, or do I try to explain things? If so, how hard do I push?' When should a good consultant question a decision, and how does the situation differ with contract programmers?"