In party games I like everybody to have a degree of versatility. I don't mind if you're a white mage as long as you have the odd offensive spell too. In the more customisable games (e.g FFVII) I tend to make everyone into a bit of a black mage. In single player (e.g Fallout) I tend to specialise more initially, only branching out when I'm starting to feel confident I've hit a decent level with my base skills. It does depend on the game though.