I was wondering i am a very self reliant person and i very much enjoy crafting my own things. Would it be worth it for leveling purposes ONLY to have every profession? I have a level 80 dk that i can use for herbalism and mining and i will be leveling all the classes and in no way in a rush to get to 80 again.
Actually, I think it's almost the other way around - it's not exactly worthless for leveling purposes, but there's much more value in feeding an endgame toon or stable of toons.
Thanks to the economics of my server (which has been on and off the "recommended" list ever since I started), I've managed to profit off of leveling all my professions - my main is herb/alchemist who fed lazy raiders, my new-80 hunter leveled enchanting through disenchanting and leatherworking by selling what had value and DEing the rest, and my druid is on the jewelcrafting cycle (buy gems to level to where you can prospect the same gems and sell them on to the next sucker).
The actual utility, on the other hand, was minimal. There are a few "sets" of leather/mail that are better than random drops/quest items of the same ilvl, but considering the opportunity cost (either in capital to buy the mats or the labor to farm them) it's not significantly different than just buying them premade from another LW.
Another way of looking at it is as a "real-world" application of the "Law of Comparative Advantage" - it makes sense for each of us to specialize in doing the things we're best at, and exchanging the surpluses with each other. The best example of this in WoW was back in BC, when certain classes were so much better at farming primals that it made little sense for anyone else to spend any time on it at all. But it is true to a lesser extent for any kind of raw material, and even for BoE crafted items. BoP crafted items are a special case, but those are (a) almost entirely endgame, (b) much rarer than they were pre-LK.