Sometimes when you check out a random book from the library, you will get a cozy murder mystery or a silly children's book; but sometimes you will get an impenetrable, exhaustive info-dump of a book on a 20th century composer whose work you are more or less completely unfamiliar with, and who seems like a bit of an acquired taste, especially for you, whose classical music taste is mostly the greatest hits - Bach "Mass in B Minor", Beethoven "Eroica", Ravel "Bolero" - things that are nice and tonal, which is not to say that you need to like the music to enjoy the biography, but it helps to have some sort of hook.
This is probably the definitive Schoenberg bio, in that it contains every single known detail about his life, but it is painfully dense, and some of the worst writing I have ever attempted to read.