Secondary skills in Heroes 3.

Here, we are only talking about the main hero. Secondary heroes benefit from taking estates, literacy, and artillery. Water spells, when combined with earth and air magic, are usually left unused, so I don't take them. Resistance... there are more important skills, and there's no room for it. It makes sense to take it if there's a chance to acquire artifacts that grant magic resistance.
Tactics is certainly a skill with mixed results. Sometimes it helps a lot, and sometimes it's useless in every battle on the map.
What makes ballistics particularly good for Barbarians? To charge into a town with behemoths?