I can't really answer your question... but 2 weeks ago a bolt securing the belt tensioner (on the alternator's side) snapped, which - in some unknown consequential order - threw the belt, destroyed my water-pump, sheared off some fan-blades which punctured the radiator... which has now drained my wallet.
I guess that the bolt snapping was the consequence of its being overtightened sometime during the car's life. If there's a lesson of sorts in this, it's that the little, overlooked, unsexy things can suddenly fail and wreak havoc.