In a recent project, I was working with someone who wanted to mark a comment as unapproved regardless of the value that was set in the WordPress settings.
Specifically, the person was using a plugin that allowed for certain attachments to the plugin. In order to make sure that the comment could be screened prior to allowing it to go public on the blog, they wanted to moderate it from the dashboard without needed to completely enable comment moderation across the board.
This is something that’s relatively easy to achieve programmatically.