Here's the part from the relevant Meta.SO answer
What is the effect of the Spam flag?
This type of flag receives an extremely high priority in the moderation queue. It should be used only when the content of the post you are flagging meets the criteria defined below, or it will likely be declined.
The spam flag is designed to eliminate posts with no relevant content and to penalize the authors:
- 3 flags (spam or offensive): post is banished from the front page.
- 6 flags (spam or offensive): post is locked, deleted, and the first revision owner loses 100 reputation.
- 1 flag from a moderator has the same effect as 6 flags from normal users: instant destruction.
- Because a question with 6 flags is locked, a 10k reputation user cannot meaningfully undelete it.
- Each spam flag counts as a downvote for calculating the post's score (it does not affect the user's reputation).
Is there any way to remove Spam flags?
There is often no need, as spam flags expire after 48 hours if the thresholds aren't reached.
Rolling back a post to a previous state will revert to the number of spam flags from that particular revision. This allows the OP (or someone else with edit rights) to rollback a post that someone else made spam in a later revision. However, as a general user, once you mark a post as spam, you cannot take it back.
How does the Spam flag differ from the Offensive flag?
There is no functional difference aside from separate counts - 3/6 of either will be sufficient for mechanical purposes.
Personally, this is what I usually do:
- Flag as SPAM.
- Edit out the spammy part.
- A mod eventually will come and look at it and check the user.