So you're a mage. You have a job, and that job is taking something that was previously intact and converting it into much smaller, bloodier, often frozen chunks of that same thing. You manufacture shattered mobs, and you take pride in your work. But you may also have a side project or two. Maybe you thought to yourself, "Self, perhaps when we aren't making warlocks explode, maybe we should spend our time sewing trousers. Or baking cupcakes. Or making necklaces."
Well, your self is right. You should be using your downtime in between vicious warlock kills to learn a side trade. They offer bonuses in the form of cool gear, extra money, and bonus stats, plus a bit of catharsis to help you decompress form all that murder. But which professions should you choose? That's easy: anything but mining. What's that? You'd like a bit more detail? Oh, fine.