There are some people out there (not me) who forgo using whole skill trees and any associated abilities because they "don't fit" with what they want their archetype to be. From what I've seen, it's mostly diehard warrior fans. It's not a bad thing exactly, but I personally would never restrict myself that much.
hell no. I've only ever even used restoration in my pure mage. Otherwise, my archer/hunter/thief only uses potions, as well as my dual-wielding warrior (who's forbidden to use any school of magic), and my necromancer (since he already does lots of alchemy for poisons, might as well brew some healing potions too)
I never raise Restoration. It's a waste, in my opinion. You can use enchantments and potions to make sure you stay alive.
Not only that its a lot harder to raise in skill because you have to actually be hurt and second, it takes precious seconds to switch spells and cast and possibly 3-10 seconds if you change from a weapon. Unlike potions which can be used instantaneously.