For exmaple: In signature campaigns, the manager might tell us about new openings, OR in some big threads like those of MERIT history, Bitcointalk updates where big debates are going on, some good announcements to be made etc etc.
You can edit the OP with the latest additions, and quote that part as a new post to bring it to the attention of existing readers.
As far as I know, there's a
limitation of length for each post. In some cases when the #1 posts reach limitation, it can't be added any new content. I think OP's idea fits those cases.