Just depends. There are some professions, like enchanting, which are very hard to level up pre-60, usually b/c you need to just go ahead and vendor items for the cash.
But I'd say it's worth doing gathering professions for the money. Maybe some crafting professions are okay to do while leveling, I've known people who finished 300 blacksmithing before they were 60. But I dunno, seems expensive and you can usually just blitz the professions later with both money and power, and even a mount.
Gensei - Shaman, Bloodsail Buccaneers