A tyrant must put on the appearance of uncommon devotion to religion. Subjects are less apprehensive of illegal treatment from a ruler whom they consider god-fearing and pious. On the other hand, they do less easily move against him, believing that he has the gods on his side.
Policy-based controls are fantastic, but you now have a separate constraint coming in from the side which is compliance. More powerful management tools give you easier changes, but then you have to beef up the audit trail and show your managers and auditors the mapping between your stated policies and the measurements coming up from what's really happening.