This subject is controversial, as most of us agree that pulling a ground is always a good idea, though not required. However, bid work on larger jobs might result in the decision not to pull a ground due to cost, or the need to upsize conduits to accomodate the additional conductor.
Any instance where either an isolated ground, as in some data applications, or an insulated ground, as in health-care or swimming pool type installations would require an additional ground. See a previous post for a thread on this topic.
