Waaaay back in the early days of Stack Overflow Jeff [wrote a blog post about the Stack Overflow Question Lifecycle.][1] 

> **Who decides what questions don’t fit?** Trusted members of the Stack
> Overflow community decide which questions belong on Stack Overflow.
> Every question goes through a community vetting process:
> 
> 1. You see a question that is inappropriate for Stack Overflow because
> it’s not programming related.
> 2. You have 3,000 reputation, the minimum required to cast close or
> open votes.
> 3. You vote to close this question.
> 4. Four (4) other users also vote to close this question, reaching a
> total of five (5) closure votes (or, a moderator votes to close —
> moderator votes are binding.)
> 5. Once closed, the question can be reopened by voting to open in the
> same manner. If the question garners five (5) votes to reopen, the
> process starts over at step #3.
> 6. If question remains closed for 48 full hours, **it is now eligible
> for deletion.**
> 7. You have 10,000 reputation, the minimum required to cast deletion
> votes.
> 8. If the question gets three (3) deletion votes (or a moderator
> vote), the question is deleted.
> 9. Note that deleted questions are invisible to typical users — but
> can be seen by moderators and users with 10,000+ reputation.
> 10. The question can be undeleted at any time by voting for undeletion
> in the same manner. If the question garners three votes for undeletion, the process starts over at step #7.

In my experience closed questions hardly ever get voted to delete afterwards. [According to this Data.SE query][2]:

- Exact duplicate 2994x
- Off topic 2444x
- Not a real question 640x
- Subjective and argumentative 481x
- Too localized 320x

So if we exclude the duplicates, which we tend to keep around, that leaves us with 3885 questions that are eligible for deletion. That's still 4% of all questions, which I think is quite a lot.

Because we don't keep negative comments, spamming users and off-topic answers around, I don't see why closed questions should be any different. So next time you come across a closed question that you think has no worth staying around (which is nearly all of them), please **vote to delete** them! That way your fellow users can help clean them up. If you don't have enough rep, but still want to help out you can **flag them for moderator attention**.


  [1]: http://blog.stackoverflow.com/2009/04/the-stack-overflow-question-lifecycle/
  [2]: http://data.stackexchange.com/superuser/s/791/distribution-of-close-reasons