First, because you can systematically learn a lot of knowledge in the training class, including current political hotspots, answering skills, scenario simulation, dressing and so on. You can't practice this by yourself. Even if you want to practice by yourself, find someone to help you record and comment. Only when you see your own performance can you understand the difference. Besides, you need to know some common sense, which you can't understand yourself.
Second, because the students who basically passed the written test are almost the same in strength, others have signed up for the class, and there are professional teachers to guide you in all directions. Think about what you need to compare with the efforts of others if you want to teach yourself. The cost and time cost of this effort, including all your own costs and your own efforts plus other things that you can't do alone, may not be cost-effective. Money, time and energy are interchangeable. If you don't want to pay, you need to pay something else, so it seems that the world is still fair.
Third, no matter how big or small the gap between you and others is, you should face it with the mentality of 12 points, and you should not be proud of high scores or discouraged by low scores. A glimmer of hope is also worth the effort. Even if you fail this time, accumulate experience and fight again next year!
Need to remind you that even if you sign up for class, you should study critically and learn your own style. The interviewer is very disgusted with the standardized candidates in the training class. When answering questions, he should also have his own thinking and style. Don't pretend to be empty, he must have his own true feelings in it, otherwise he will lose points.