A good contractor is in constant demand, and many homeowners believe it's worth putting up with odd hours and extended projects to make sure the job is done right.
However, even if your contractor does good work, there's no guarantee that his subcontractors are equally well-trained. In fact, many horrified homeowners have hired reputable contractors who sub out their jobs to a novice workforce that changes on a daily basis. The contractor will still stop by for a few hours here and there, but he might not be providing the kind of guidance you expected and paid for.
To prevent this from happening, ask your contractor if he'll be subbing out any of the work. If he plans to, find out if you can expect to see the same people working on your home every day.
If your job requires an on-site supervisor, you should ask to see some of that person's work -- he will most influence the labor that goes into your home.