Dragoon is a job, not a class, meaning anything they get, can be used by their base class, which is Lancer. so anything your lancer can use, will transfer to Dragoon. This also means that dragoon will not level up or gain experience. Instead any experience you gain, goes back to that job's base class, which is lancer for Dragoon. So there really is no reason to not use a job, unless you're intent it to use a myriad of cross class skills(as jobs give you access to only 3 class skills, the base class, the secondary, and one other).