We had 'Prep' at our school. It was quite diverse in what it achieved. For those who needed time to study without being disturbed, it provided "quiet" time. It also provided group learning as we would all be sharing ideas and getting feedback on our homework all at the same time. If you missed something in class, you could guarantee someone else knew what was discussed.
It was also a social event where everyone was together and, granted a little forced, but we all interacted.
If you found it 'dreary' you would try and get some sleep.at your desk or do something disruptive. With a Teacher providing oversight it become more of a game trying not to get caught.
Lots of fond memories doing 'prep'