Right now very few members use the flagging feature. We can use "flag as spam" to clean up the front page. If a question is marked as spam by enough users it will get closed and will not appear on the front page anymore.
But we don't actually have spam questions. Misguided, badly written, yes, but spam ? I'm not comfortable doing that, because a question that gets closed as spam has serious consequences for the user posing it. I think they get temporarily suspended, and lose 100 rep, and some other things.
Also, flagging sends a message to the moderators. Once we get our own, it might be useful, but not right now.
Update: here's the official statement of what happens when a post is flagged as spam:
Don't do this for questions that should be closed, that is, off-topic, dangerously argumentative, &c. You can flag them "Requires Moderator Attention" if they are worse than usual questions in need of closing. Questions get automatically deleted when they have been flagged spam often enough, which is not the right outcome for such questions: closing or even locking is.
When is a post: