At first, Craftsman seems like a great pick because it's what actually lets you actually produce goods, and if you're the one to pick it you can often produce more than everyone else. However, producing goods isn't the goal of the game, and what matters is what you can do with them. If you pick craftsman, you are nearly guaranteed to be the last player to USE your goods, even if you have more.
That said, when would picking craftsman actually be the best choice if you're just letting your left hand opponent ship/trade his goods first? Obviously if there's a nice stack of money on it you'd probably want to grab it, and if you have the right combination of goods that you are still guaranteed to trade or ship what you want to then it'd probably be fine.
When is it okay to pick Craftsman? How can I explain to beginners when they should and shouldn't do so?