Possible Duplicate:
When should I vote to delete?
I've been getting a lot of privileges lately, and I don't really know how some of them should be used.
For example, voting to close a question is clear enough, but when should a question be marked for deletion?
I don't mean the obvious spam that may arise (not that I've seen any yet, myself), but actual questions of low quality. How bad does a question have to be for it to be deletable?
The FAQ helps you a bit under the section "Why are some questions or answers removed?" stating that:
Questions that are extremely off topic, or of very low quality, may be removed at the discretion of the community and moderators.
Over time, closed questions that are not useful as signpoints to other questions may also be removed, as well as questions which have no significant activity over a very long period after being asked. For additional guidance, see How to Ask.
Every site has this section, I'm taking the MSO FAQ as an example.
So, apart from duplicates — which are usually those signpoints1 the quote above refers to — other questions are deleted after a certain amount of time.
In summary, the most common types are:
1: Duplicates are useful even when closed because if a new user finds the duplicate, instead of the original, this will prevent another "dupe's dupe", pointing that same user to the original question.
Generally questions that are deleted are those questions that are not useful for the site where they are asked, such as off-topic, not constructive, not real, and too localized questions.
Duplicated questions are generally not deleted because they can help who is searching the duplicated question. Clearly, if a user submits the exact same question twice, the newer question is closed, and deleted (or directly deleted from a moderator).
