Today I saw this question and flagged it as Very low quality because as far I know, it doesn't belong here and should be closed or should me migrated.

I usually flag a lot of questions as Very low quality and my flag is marked as "helpful" when the question is migrated). But my flag was declined and I got -10 flag weight.

The moderator said:

"declined - question has details and is clear; only thing off is where it is located, nothing speaks VLQ"

I don't agree. Even if it was migrated, it was a very low quality for SU.

As this post says:

Flag actions are applied to all users who flag a post, regardless of what they flag it with. Any moderator action such as closing or deleting a post will automatically mark all flags as valid. If the moderator manually marks the flags as valid or invalid, that action applies to all flags on the post.