#4 - July 7, 2014, 11:05 p.m.
Crafting will do a great job of filling in the gear gaps you may have while leveling up, and it has several important roles for level 70 characters as well. Personally, I think it's a great idea to keep your artisans up to speed while you level, and definitely recommend doing so.
They'll provide you with a variety of ways to upgrade your gear, utilize resource materials that would be worthless otherwise, and best of all they only needed to be leveled once. The artisans are shared between all of your characters of the same game type (Normal vs. Hardcore), so once one of your artisans learns a recipe then all of your characters can potentially craft it.