According to the author's usual teaching observation, some students don't have a special draft book, so they can grasp whatever they want. They use their hands, textbooks, the cover of exercise books, and even the class desktop that can write. Random "drafts" make students' thinking process disorganized and even affect the accuracy of students' calculations. Especially in senior grades, a problem cannot be solved in one or two steps. There are many steps and complicated process. Maybe a small step in the middle is wrong and it will fall short.
At this time, the well-organized draft has the advantage, and mistakes can be found through the draft, but the draft written sentence by sentence can't be found, so we can only reconsider it and waste a lot of precious time. At the same time, in order to save paper, students usually write like mung beans. Sometimes it is difficult for students to recognize the handwriting they just wrote, let alone find mistakes later.