Closed questions are a stage towards deletion. If the question indeed does not belong (thus, solidly nigh any close reason that isn't "duplicate"), then after 2 days, it can be deleted. If it's really dangerous, it can be torched earlier. Otherwise, the natural traffic will push it off the front page until it can be deleted.
Closing isn't infallible, though, that's why there's a 2 day life period. This is a period of time for users to reopen a question that was incorrectly closed, or for the question to be revised so that it can be reopened.
Also keep in mind, a question with -4 score or lower does not show up on the front page. Things that are closed as "off-topic" or "not a real question" even get an automatic downvote from Community. As such, if you see a dangerous question that should be closed and deleted, you can expedite its removal from visibility by downvoting it. After all, if it does not belong on the site, surely it does not provide usefulness to the community?
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