There are hundreds of different strategies for making money once you've hit level 85, right? Max-level professions tend to be strong money-makers in the right hands, because they allow you to sell the latest and greatest items.
It's a bit of a different story while leveling, however. There are gathering professions, of course, and some can provide fledgling characters with a solid chunk of cash. There are crafting professions too, but often times low-level gear and items sell for less than the materials it takes to make them.
Making money while leveling isn't typically at the forefront of your mind when you're making your fifth alt on your home server -- after all, you can make more money running dailies at 85 than you can farming Wool Cloth. But if you're just starting out in World of Warcraft or are starting fresh on a new server without any of your main character's bank ... well, finding a way to make money while leveling is exceptionally important, especially so you can buy the much-needed conveniences that rich players take for granted, such as Flight Master's License and Expert Riding.