I can provide details in Taiwan. I know the situations in many other countries in Asia are similar. Hopefully users from Asia on this board can confirm this.
In Taiwan, the role is called class leader in elementary school, middle school and high school. They are usually assigned by the teachers of the classes.
In college, it is called the class representative. The representatives are elected by the students. The length of the term usually is a year.
Upon entering college, students already select their major. The university groups all the students having the same major into one or more classes depending on the number of students (the standard class size is 50). They take all the required courses together if possible. The students in the same class know each other very well. The class is like a big family. Naturally, you have a representative who speaks for the class and handles all the administrative matters. You also have a deputy representative in case the rep is not available. There are other students responsible for other duties such as purchase, sports, etc.
The rep gets elected usually because he/she is popular in the class or a good student. I would not say he gets preferential treatment from the professor/department because he is the rep. Sometimes it is the opposite. I once declined a rep nomination because I wanted to concentrate on my study.
However, being a rep can be advantageous. You learn how to be a leader. You learn how to communicate with other people who are sometimes superior, such as the professor, department chair or even the dean. Leadership is not something you can learn it all from the books. You have to do it. Two of the four reps in my college class are very successful in their late career.
It would be much easier for the professor to talk to the class rep when he wants the whole class to do some unusual assignments. Once you can convince the rep it's the right thing to do, the rep would then pass the message to the whole class. You are more likely to get the cooperation from the students. I would not recommend you to use him very often, though. He represents the class, not you. He would lose the trust from his classmates when he becomes your pet student. In general, the class representative concept is more like the department chair of a university department.
Hope this helps.