Let's look at flagging on a more hedonistic level.
Flags should be used (and are often marked valid) when:
- you spot disruptive user behaviour (sock puppets, cussing, reposting, etc.).
- a post needs shifting to a site not in the default migration paths.
- a post is undergoing an edit war (a moderator will lock if/when necessary).
- someone posts an answer that is really a comment or a new question but they failed to see where the upper right corner of the screen is.
- comments on the post need clearing out (you can usually just flag one comment and explain the nuke request).
- you are under the rep threshold of whatever action you want to carry, be it close or protect.
- a user needs merging.
Flags should not be used (and are often marked invalid) to:
- say a post needs editing. Everyone can do that now. Be bold.
- downvote a post. Just downvote it already.
- have conversations. Try chat instead.
- leave cryptic and/or vague messages about what to do with the post. Flags like how something may be a duplicate, but you just can't put your finger on it don't help.
- vote to close by proxy when you don't want your name to appear on the close list.
Borderline dismissal usually hangs on when a post is flagged for migration when it is either:
- fine to stay on the site as is.
- doesn't meet quality control standards. As in, it's not junk waiting to flush back up the septic tank. We try not to send other sites crap questions just because the content may suggest it fit better. If it's a mess, we spike it here and be done with it.
How the flag falls in the last section depends on how the moderator at the time wishes to handle the flag. Could go up, could go down.