Surprisingly, if you choose to not follow a forum, it still appears on the list of forums you have posted in. It seems pretty clear that if someone does not want to follow a forum, most often they won't want it cluttering up the list of forums they have posted in either.
(As well as changing the effect of unchecking the "follow" box, It might be useful to add an option somewhere to make unfollowed forums visible temporarily in this list, as more rarely someone might want to check forums they have posted in even after they have stopped following them).
Surprisingly, if you choose to not follow a forum, it still appears on the list of forums you have posted in. It seems pretty clear that if someone does not want to follow a forum, most often they won't want it cluttering up the list of forums they have posted in either.
(As well as changing the effect of unchecking the "follow" box, It might be useful to add an option somewhere to make unfollowed forums visible temporarily in this list, as more rarely someone might want to check forums they have posted in even after they have stopped following them).