Bottom line is that even when the book is not deceiving you (traders aren't backing away and painting the tape, or the book isn't being updated so slowly that it's useless), THE BOOK STILL CAN and WILL NEGATIVELY ALTER one's trading sometimes (usually more times than not) just by giving someone a very misguided picture of the strength or weakness, and this is why so many top traders who can or do have access to it choose not to use it.