It gives you an option of a secure trade with a crafter rather than you just giving them your rare and hoping they can be trusted. In most cases it was fine and you got your final product but every so often the player never got the item they requested. So now its all done in a few simple steps while you wait. For example say you want a spell made. You contact the crafter and meet up with them. They initiate a special kind of trade with you which is started from the requested spells recipe. The window lists all of the components required for the spell, payment options and the final product information. You can then add the components and payment to the ui. Once both of you accept, the tradeskiller will make the item and you can watch the progress. On completion of the item the trade is finalized with the crafter getting payment and you get your spell.
This way its secure so the tradeskiller can't disappear with that uber rare item you got never to be seen again. Also they can now work on no drop or attuned items you might have which wasn't possible before.
That's actualy quite a scoop, and I hadn't heard this before.
