The first one is a purely theoretical course, which means it doesn't matter if you don't listen for a semester. It doesn't matter whether you listen or not. Anyway, in the last week of exam week, the teacher will draw a lot of exam ranges. Then you can recite it yourself.
Second, you can listen or not, such as English, advanced mathematics and so on. English is self-accumulated, and attending classes ... is just a form. I never listen to advanced mathematics. By the last week, I could only remember some formulas.
Third, it is the kind of course that must be taken. For example, accounting, this accounting subject and accounting subject, if you don't take a class, it will take twice as long to understand it after class. I don't attend several classes, but I have to attend every class. Otherwise, you have to take the exam again.
The above is my three years' experience in college, but to be honest, if you are still at the beginning of college, or haven't finished school, and don't go to class, don't spend your time playing cards and games in the dormitory. Take time to improve your English, or specialize in your major. This will be very useful for your future work.