I like the idea of only one forum for coupons, so you don't have to check in three different places. The only time I would even think about checking for coupons would be near the expiry date, so they would not go to waste. My vote is for 1 coupon forum, with monthly expiry dates.
It also occurs to me, that even if posts are "edited to nothing" you still might end up with a gazillion empty posts. A monthly forum would "self empty" every month.
I still like the idea of removing items once they have been used.
Regards,
Ken Hamer