Pre-class reading is a relatively important part of your in-class learning process. This is because to have an enjoyable learning experience you do need to have some prior context of the materials that you will be taught in class. Doing pre-class reading will usually help you understand the concepts being taught as they are generally used as case studies. Knowledge of the contents of the reading will meet the lecturer’s teachings half way for you to fully understand the material. This is a very common case in social science courses such as politics or history as they usually learn about theories based on events that have happened in real life. Additionally, the moment when you have any confusion after doing the reading and the lecturer explains exactly what you were wondering can become a particularly euphoric experience as its relatively rewarding.
When doing pre-class reading, taking notes is an helpful method in understanding the contents. By taking notes, you don’t have to memorise the contents of the reading and can refer to your notes when the lecturer is explaining or when you want to keep a question in mind to ask during class. Doing this is particularly useful for students whose grades are in danger of failing as it is effective and the panic these students experience are probably sufficient catalysts for them to expend more effort to study.
Despite all of this, not doing the reading would not be the end of the world. Lecturers are generally rather lenient and would not publicly shame you for not knowing the contents of the assigned reading. They would probably let it slide but you would probably have to do extra revision compared to your friends that were more well-prepared for the class.