When someone speaks of an exhausted vanilla bean, they are a referring to a bean that has already been used. That doesn't mean it is completely void of flavor, however. An exhausted bean that has been used to develop 2-4 rounds of extract might be considered spent when it comes to releasing its flavor into extract, but it could still be ground into a fine powder to deliver a subtle vanilla flavor elsewhere. Likewise, pod that has been scraped of its seeds might be said to be "exhausted", but it could still be used to impart flavor into vanilla sugar or extract.