Popular classes may have many hundreds of students enrolled, and schools may not have classrooms large enough to fit all the students in. Professor time is fini

Popular classes may have many hundreds of students enrolled, and schools may not have classrooms large enough to fit all the students in. Professor time is finite and may not scale to giving duplicate lectures, supervising tens of TAs and deal with the 5% of students who demand unusual attention. So schools offer multiple sections of the same class to share the workload. E.g. in recent years Computer Science 101 - often the most popular class on campus.