Each semester class only meets for a quarter. Following is a list gleaned from my experiences. A teacher sees less students during the day, thereby giving them the ability to spend more time with each individual. Because of the increased span of teaching time, longer cooperative learning activities can be completed in one class periods. Also, there is more time for labs in science classes.
Students have less information to deal with over the course of a school day.
Because of the decreased number of classes, students have less homework on any given day during the week. The teacher is able to provide more varied instruction during class. Thus, it is easier to deal with students with disabilities and differing learning styles. Planning periods are longer. It seems that with a longer span of time, planning becomes easier and more gets done.