Leatherworking, as the name implies, is the crafting discipline able to create leather armor. This can be especially useful if you are an Engineer or a Thief, as you’ll be able to make use of all the items that you craft. There are also bags and other miscellaneous items, such as runes, that can be crafted to help augment your gear or to sell.
In traditional MMOs, items are the reason for playing the game, for griding through dungeon after dungeon to obtain the highest-level gear possible.
Given the fact that Guild Wars 2 challenges this by essentially removing that gear grind, the role that all items play in the game, armor and weapons, takes on a different meaning.