As an exam, his method is very good, which can effectively save thinking time and get the results quickly and accurately. His method was actually used by many people in the exam. But on the other hand, his method also has limitations, so it's hard to say about slightly difficult questions or clever answers. Another point is that his method is best used only when checking the correctness of his answers in exams or usual exercises. Because his method can only be an answer for people with poor foundation, but I don't know why. If the same topic is a question and answer, there is no way out.