A reason
A reason for contrasting views on Beyond Counting. (Certain other posters seem to be stuck on discussing Beyond Coupons, but that wasn't L4Count's question.)
Grosjean devotes much of the book to deriving the theoretically-optimal strategies for exploiting extra information in various casino games. He also develops more practical or simplified strategies that a player could more easily implement at the table, or that could help the player avoid heat. The analysis is often comprehensive and in-depth. True, it sometimes extends to levels of information that you'd be unlikely to acquire.
However, Grosjean has relatively little to say about the methods by which you might acquire such extra information. For the most part, he limits himself to listing the potential methods by name, and saying which are legal or illegal, or if the question is unsettled, might not be legal.
Some players believe that they have no chance of acquiring the extra information needed to take advantage of the book. Those players consider it worthless. Other players have found situations in which they could get that information, and find value in Beyond Counting's strategies. My opinion is that an aspiring AP should remain open-minded.