The Burning Crusade brings a couple of things to the table where professions are concerned. In addition to new recipes, schematics, patterns etc, several professions receive specializations.
Before BC, only a couple of professions had specializations. Specializing gave you access to a branch of new craftable items, while blocking off access to other branches.
The “New” specializations in BC provide different benefits, such as the Alchemists” “Master of Potions” allowing you a chance to create multiple potions per combine.
In addition to the new specializations, BC introduced another feature; Recipe Discovery. While crafting, you may learn a new recipe out of the blue. These recipes can only be learned by discovery, and the chance of it happening it extremely small.