Alteration is nice for any character to have (I think... Been a while). The rest are all more for doing just one thing (IE: Alchemy makes potions, Destruction hurts people), but it's mainly Conjuration that I'll go so far as to leave out of my mage custom classes. Though, Enchant is my second favorite, still nice to have it as a major skill, since super enchantments aren't cheap, and I like super enchantments