Pros
Ethical, genuinely concerned with producing a good product; as with any contractor, you are often not that involved with your employing company. In my case, I was, and the interaction was professional, if slightly detached.
Cons
For many past jobs, I have felt more included in the decision making process (regarding hiring, project level decisions, customer interactions). Here, I felt like I was more informed about a decision, even in cases where I felt I had the expertise and probably should have been consulted.