Welcome to the Metadata Millennium: A Complete Overview of What Metadata Can Do for Publishers
And of course the publisher wants to include marketing metadata -- that's what helps the book sell. Subject metadata has always been used for physical books to guide the bookstore as to where to shelve the book. For ebooks, subject metadata is even more important: it's what enables users to discover books on subjects they're interested in. But marketing metadata can include a lot more, such as reviews, prizes the book has won, a bio of the author, other books by the author, and other books on the same subject.