From How do I properly use the "Not an Answer" Flag, Robert Harvey stated the following here which I have quoted:
What is the Not an Answer Flag?
The Not an Answer flag is a moderator flag that community users can use to notify moderators that a posted answer is not an answer, and should be deleted.
What is the purpose of the Not an Answer flag?
To identify attempts by community members to use answers for any purpose other than answering questions.
When should I use this flag?
Use this flag when an answer is being used to:
- Ask a question
- Communicate with another user
- Say "thanks," or confirm that another posted answer worked for him.
- "Bump" the question, as in "I have the same problem, have you found a solution?"
When should I not use this flag?
Do not use this flag when:
- The user posts a partial answer
- The answer is wrong or inaccurate, or you disagree with it
- You have to consider the question, other answers, or even the comments on the answer itself in order to determine if an answer is not-an-answer
But I'm still not sure if I'm using the flag correctly ...
Then cast a moderator flag using the custom option instead, and explain why you >think the answer is harmful to the site, and should be removed.
In regards to how flags truly work, I am not sure if anyone really knows. I have asked a few questions on math.meta with links to meta on this topic a few times. Your fearless mod @madscientist even tried to get action with a bounty here but nothing came of it.
- What is the difference between disputed and declined flags?
- What is a disputed flag?
To summarize, I have been told by mods that a declined flag doesn't mean a mod handled it; however, a decline can come from a mod handling it. Then you read from meta it should have been marked disputed since the community review was in contrast to your flag. So why some flags are declined vs disputed and who handles them seems unclear. Who knows if anyone knows how the flags work 100% of the time.
From How does deleting work.., the following answer declares that:
What are the criteria for deletion?
For questions, a post that no longer adds anything to the site should be deleted. Basically, this includes most closed questions that cannot be improved and reopened. However, it may be beneficial to keep duplicates to aid future users in finding the canonical question.
For answers, any post that is not an answer (should be a comment, doesn't answer the question, etc.) should be deleted. Answers that are wrong or that dispense poor advice should be downvoted, not deleted.