There are many, many circumstances in which computer-matched ads might not be a good fit. Imagine if a site for entomologists somehow got stuck with ads for Volkswagen Beetle parts, for example. Or if a site meant to showcase funny pratfalls was paired with ads for vacations ("trips"). Fortunately, Google's testing expanded category blocking with AdSense. The category filtering beta used to offer sites' owners a way to turn down ads from up to five categories. It was meant to be used in a rather broad fashion.