Why don't we delete these instead of closing them?
- To serve as an example of what is off-topic here. The rationale is that people who see off-topic questions closed remember them and don't ask any off-topic question. The same goes for "bad" questions (i.e. "not constructive" ones).
- For historical purposes (some people really want these to stay, which would lead to delete-undelete wars)
- As a stage prior to deleting (e.g. you can go through all the "Not a real question" questions and delete them sooner or later)
- etc.
And when is is appropriate to delete a question?
When it is …
- absolutely off topic
- insulting, offensive
- spam
- not valid anymore
- of really bad quality
- etc.
The reasons vary here.
See this blog entry for more details:
The Stack Overflow Question Lifecycle
Why do you allow content to be deleted?
Just like death is an unfortunate but normal part of life, I believe deletion is also an unfortunate but normal part of living websites.
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Why would you delete a question? Isn’t closing it enough?
- Some questions are of such poor quality that they cannot be salvaged. They’re literally nonsense. Not every byte of data that is created in the world is infinite and sacred.
- Some questions are so incredibly off topic that they add no value to a programming community.
- The mental cost of processing these closed questions is not zero, particularly for users who are actively engaged and scanning questions to find things they can help answer.
- If users see a lot of closed questions, they’ll note that we don’t enforce the guidelines, so why should they? Without any final resolution, asking questions that get closed becomes something we are implicitly encouraging — a broken windows problem. If this goes on for long enough, we’re no longer a community of programmers who ask and answer programming questions, we’re a community of random people discussing.. whatever. That’s toxic.
- If enough of these closed questions are allowed to hang around, they become clutter that reduces the overall signal to noise ratio — which further reduces confidence in the system.