If she was forced to respond and solve things right away, then it was better to handle such matters with the aid of such knowledge, especially when it was the type of situation that would have some relation to any of the things that would be covered in the book.
If she could make use of the experiences described in the book, then that would help her greatly to overcome any situation that she had never experienced before and was not familiar with.
If she encountered a situation that she had never encountered before or could not have anticipated, especially when it was related to what she could experience when being involved with Cerberus or being influenced by the criminal underworld, then she needed something to rely on.
If she did not have such things, then there would surely be a time when she would be caught unprepared, and that would cost her greatly.
