The question of whether to buy or gather your own materials is a matter of fierce debate, but really, the answer depends on what your goal is in the game.

If you're reading this book, then you probably want to have a big bank balance, but is that your only goal? If money is your only motivation, then you'll probably find that buying materials, turning them into finished products, and selling them on for a profit is faster than gathering your own materials, at least if you can find the right recipes.

There are some craftable items that do not command high prices. In fact, if you bought the materials, you'd make a loss. You could skip those items, and continue churning out lower-level items that give less experience, or, you could gather the resources that you need and make those items, selling them for some money, but less than you'd have earned if you just sold the ores/wood/plants/ other required resources.