you can use onagers very effectively to drive opponents off of strong defensive positions as someone else pointed out allready, this works equally well for multiplay and sp. i disagree that onagers are too accurate, they are only accurate at all when firing stone boulders, and these will only kill 1 or 2 men with a direct hit, in order to score any substantial kills you need to use flaming ammo and that is wildly inaccurate, a smart enemy will close with you before any random hits mess up his lines.