When doing Cannith crafting (the stuff in the House K or House C crafting hall), you make shards to get crafting exp to make better shards and so on. You need to make a LOT of shards to max out crafting.
Some shards are cheaper than others at the same level to make, and so you want to focus on these shards for preference. The problem is that the exp you gain for making shards decreases each time you make it. If you TR, the game forgets which shards you've made before so you can craft the cheap / effective shards for full crafting experience again. This makes maxing out crafting a lot cheaper (although a lot slower as well, of course).