(If you browse a chan, you'd certainly know about this.)
In other words, give us the option to choose whether our replies would bump a thread or not. Believe it or not, what if we don't want to bump a thread we think is inflammatory or stupid, but we want to reply? Cue sage. (This would also make post ID gets viable, but that's not really the point I'm trying to make.)
(Sage posts may also count for less points, and a sage reply to your own thread would get something like 0 points, for example.)
I WON A BET AGAINST AZUREN! WOOOOOOOOOOAAAAAAAAHHHHHHHHHHHHHHHHHHH
:3