I've used the induce rioting bit a lot, but not in preparation for an assault. It's to hurt an enemy I'm not going to be assaulting in the near future. If the city revolts, it's going to go from what may be a 6-10 unit garrison to an 18-20 unit garrison, mysteriously even though you may have destroyed every single building in the settlement that can recruit troops. In my current game, Spain did extremely well, in that they owned all of the spanish peninsula, all of France, and had taken Antwerp, Metz and Genoa. Genoa was their last conquest. The turn we shared borders (I owned the rest of Italy except for Milan, where the Papal States had been displaced), they attacked me. I made Marseille revolt. Then I shifted north, and caused Dijon to revolt. Then I made Paris revolt. He's too busy trying to retake the cities that revolted to send any more armies at me, and in the meantime I loaded an army on the boats, sailed west, and snagged Toulouse out from under his nose.