Guide books or book notes are primarily written to make students understand the original text better, especially from all those angles which are often overlooked by a casual reader.
But, in the recent years it has been noticed that a very large majority of the students, without reading the original texts, rely on the guide books or notes prepared by their teachers or others. This is definitely not a healthy habit because students do pass their exams with the help of such notes; they miss so many things which haunt them in their later lives.
I would strongly advise all the students to read the original text once again even if you have already read it,