Imagine a MMORPG in which the best-in-slot items are crafted from cheap, vendor-sold materials, by just a click of a mouse, without requiring hard-to-get recipes. It is easy to see that such a system would quickly ruin a MMORPG economy, and the other gameplay as well, as there would be less motivation to go adventuring if crafting was so easy. Crafting needs to have *some* limiting factor to prevent players from getting too good crafted items too easily. But you can think of different crafting systems each using a different limiting factor.
The system of World of Warcraft uses mostly resources, and to a limited extent access to recipes as limiting factors for crafting. As resources are needed not only for making the items you actually want, but also the items you just craft to skill up, this has led to an economy where the low- and mid-level resources are worth *more* than the items you can craft with them. Crafting is extremely unattractive for new players, they are better off just taking gathering professions and selling overpriced resources on the auction house. On the other end of the spectrum are twinks from characters with thousands of gold, which just buy tons of resources and level up a profession from zero to mastery in an hour. The act of crafting isn't valued at all, many players are outright angry when they bring the mats and the crafter demands a fee. As resources are tradeable, the whole WoW crafting system with resources as limiting factor doesn't scale very well.
At the level cap of WoW, people don't buy resources any more to skill up, so crafted items are worth at least as much as their resources. But if you look at the whole value chain, you quickly notice that the biggest crafting profits are done at the steps which have a cooldown. An alchemist for example can make 100 gold in 5 seconds every day, by transmuting rare gems into epic gems. Patch 3.3.3 removed the cooldowns for cloth and titansteel, and prices for those items dropped sharply. Items with cooldown are valuable because you can't make unlimited quantities of them, remove the cooldown and supply rises to meet demand, crushing profit on the way.
Thus I was thinking that a crafting system limited not by resources but through cooldowns would work a lot better than the World of Warcraft system. Instead of having 450 skill levels there could be just as many as there are levels, 80 now, capped at the character level, and every item would at least take 24 hours to craft. So new player or twink would both take at least 80 days to master a profession. Blue items and purple items could take longer to craft, lets say 2 days for a blue and a full week for an epic. There would be less items crafted just to skill up, and more that are actually useful. Crafting a really good item would have value beyond the cost of the resources. And as crafting was limited by those cooldowns, there could be more items along the level curve where crafting them would be a good alternative to hoping for a drop from a dungeon.
Basically cooldown-based crafting is fairer than resource-based crafting, because you can't just buy your way to the top. Players have vastly different amounts of gold and resources, but every player has exactly the same amount of time per day. By limiting the output, crafting could produce better items, making crafting more interesting, without killing the economy.