In our school, everybody is doing it. At year 13, you can drop it if you want. Nonetheless, people who have grade C's and above must continue, while people who get grade D's and below can't continue.
It's a waste of time. You just do past papers. Furthermore, the only good thing is that you get to discuss/debate about things.
These days, some of my friends skive these lessons last year and this year as they always do the same things. Nevertheless, they still got a good grade in GS last year.
The teacher doesn't even care if they skive or not.