My main is a jewelcrafter and an engineer, and neither of these professions were learned for anything other than giving myself a boost. I've had engineering since I created the character back in Burning Crusade, but I've flipped my secondary profession around a few different times to something I felt would be useful -- in Wrath I had leatherworking for a short period of time. I seem to have settled on jewelcrafting as a semi-permanent one for now though, mostly because I always need gems for something.
I admit, I'm not much good at making gold in World of Warcraft.
Patch 6.1 introduced a new trait for garrison followers -- the Treasure Hunter.