[Baalz]

Well, if you have more than 3 priest bloodhunting in one province you need some way to reduce the unrest other than dropping the tax rate because you'll accrue unrest faster than a 0% tax rate will relieve it, and unrest reduces your ability to blood hunt (at 200 unrest you can't get any blood slaves). If you're desperate to concentrate your blood hunters (perhaps you're being aggressively raided) you can stack many blood hunters in a single province and have it patrolled by a large force. The downside here is that this will fairly rapidly deplete the population in that province.