“(…) some facets are useful in fundamental decision making. These browsable facets should enable their selection in the absence – and instead – of a category, then once selected, intersect with other facets using the same category taxonomy the rest of the Web site uses. Some Web sites get this wrong by not allowing pivoting to categories at all. Others try to simulate this functionality by creating a separate category taxonomy for each brand – and they fail.”

(Jaimie Sirovich a.k.a. @SEO_Egghead ~ UXmatters)