There are various settings in regard to posters who've come under moderator attention for some reason. Could be things like swearing, abuse, flaming, harassment, posting inappropriate content etc.
The lowest level is "watched". If further transgressions occur it could be raised to "moderated" in which case posts need moderating for a certain period. It automatically decreases each day until it cancels out. More serious concerns, and refusal to abide by moderators requests,goes to "sit in the corner" which requires all posts to be approved by the mods before publishing. It doesn't decrease each day like "moderated" does. It's a good system that came with the SMF upgrade.
In the past posters might have been suspended or banned but this way they have the opportunity to continue contributing while the mods can ensure posts don't breach the posting guidelines.