My previous boss, who offered me a CTO position a couple years after having been hired as a freelancer, said the thing he appreciated from me the most was that I wasn't afraid to say "No, Paul. Let's not do that. Here's why."

Sometimes the boss has a bad idea, if you're the tech guy it is your responsibility to decide if it has legs or it's a waste of time. Many consultants say yes to anything because even wild-goose chases are billable. But honesty and integrity tend to pay off in the long run, IME.