What are the actual guidelines for deleting popular off-topic closed questions?

Question

I recently noticed a relatively popular question (34 upvotes on the question, 42 on the top answer) get deleted on Stack Overflow (https://stackoverflow.com/q/29876518/1108305). This question was closed since it was pretty clearly off-topic for the site, as it wasn't about software development. The popularity of this question also wasn't merely historical: a significant number of upvotes to both the question and answer occurred after the question was closed for being off-topic, meaning that it was still providing perceived concrete value to users. This particular question was deleted by seven users casting deletion votes, so clearly it was perceived by a number of users to be worthy of deletion.

Both the Stack Overflow help center and the Stack Exchange help center list only one primary criterion for when to delete questions: ones of no lasting value.

Closed questions that are of no lasting value whatsoever should be deleted.

There are additional caveats about being cautious about deleting questions, but they seem to narrow down that focus, rather than broaden it to include more categories of questions to be deletable.

However, if an off-topic question is popular, it clearly has had value to a number of users, as they found it helpful enough to upvote. In this specific case, it was still receiving upvotes post-close, so it clearly still had concrete value to current users. So either I'm misinterpreting the meaning of "no lasting value" overly broadly, or there's more reasons to close a question than just lack of lasting value.

Doing some searching on the SO & SE meta sites didn't turn up a ton of questions that were tagged with both closed-questions and off-topic, let alone ones that dealt with popular questions specifically, so I don't know that this has been discussed too much over the years (or if it has, I'm just searching poorly).

The only noteworthy one I found was how to deal with link rot caused by deletion of popular off-topic questions?, which discusses the consequences to external links to deleted popular off-topic questions. A notable thing about this is that it treated deletion of off-topic questions — even notable ones — as a desirable thing, and apparently something self-evident enough as to not need explaining or defending:

While I am all for deletion of off-topic questions, I am not comfortable with some consequences related to the way how it is done now.

With that all being said, what actually are the Stack Exchange guidelines for deleting closed popular questions in specific, and closed questions in general? Is there more to it than just it having "no lasting value"? As someone who is getting closer to 10,000 reputation on Stack Overflow and the associated privelege to delete and undelete questions, how would I know whether a particular popular off-topic question should be merely closed, and which should be deleted?

Given the identical guideline text between the Stack Overflow and Stack Exchange help center, it feels likely that this may not be a site-specific issue, and the general guidelines might transcend a specific site. Though I could of course be wrong in this.

Note that Should we allow a mere 5 reopen votes to nullify any number of delete votes? doesn't appear to answer my question. That question is asking how to ensure the voting system works as intended to delete undesirable closed questions. What it doesn't cover is the point of this question, namely what qualities a question should have to be considered for deletion. Put another way, the other question works just as well if we presuppose a question should be deleted; it doesn't particularly seem to change based on the criteria the community feels should be used to determine deletion-worthiness.

Specific example

I don't want to distract too much from the general question with the specific example I encountered. The very short version is that this closed question was closed as being a general computer use question, rather than being a programming question. It being off-topic is certainly the case, as it was around how to download a particular type of multi-document video format. If you want more detail than this, you can check out the edit history for this meta question, but I don't want to throw the discussion off-track by getting too into the specifics of a single question.

Answer 1

Question where one can cast delete votes, is eligible for deletion

Closed questions that are of no lasting value whatsoever should be deleted.

This is the official guideline for deleting questions. There are no other rules or guidelines. Any question where users can cast delete votes is eligible for deletion and anyone can cast those votes as they see fit. Popularity, score or number of views, is not relevant in assessing lasting value to the site.

Note: When it comes to the deletion, the whole Q/A pair is being judged and question in context of this answer does not necessarily mean just a question.

Lasting value

Even though people can cast votes as they see fit, the main factor will be determining the lasting value of the question.

For some questions determining no lasting value will be more obvious, for some less. Also different people will have different opinion on whether any particular question has lasting value or not.

There are two basic types of closed questions:

• Duplicates
• Off-topic questions that don't belong to the site (this includes all other closed questions that are deemed off-topic by the site rules)

Good duplicates represent signposts, pointing people with different questions to the canonical answer to that question and providing lasting value to the site. Duplicates also get deleted, but if the duplicate of on-topic question is highly upvoted or visited, then it is more obvious that it represents good sign post and therefore it has lasting value.

Closed off-topic questions, while they may be helpful to people landing on them, which is indicated by the votes, generally don't provide lasting value for various reasons.

However, some of the questions that are not blatantly off-topic might be edited and made on-topic, so this aspect is also considered when casting votes. If the question is potentially salvageable, then deleting it is a less appropriate option.

Another, probably the most important part when determining the lasting value are the answers. The question itself, if not answered, has very little value. Quality of answers can also make the difference between whether some borderline question is salvageable or not.

Occasionally, moderators will lock such popular but off-topic questions, to prevent deletion, but IMO questions that deserve and are good candidates for such lock are extremely rare.

Why closed off-topic questions don't provide lasting value?

General points for all closed questions:

• A closed question cannot receive new answers - Inability to add new answers significantly reduces the usability of the question. While some updates can be added through edits and comments, there are limits to the extent of such edits, unless the answers are Community wiki and can be more freely updated through community effort. For questions that would be on-topic on other SE site(s) that is an additional incentive for deletion, as the question that could be alive on other sites is basically dead on the current one.

• A popular off-topic question is an anomaly - Off-topic questions can become popular only because it was not appropriately moderated in time. That does not point to the value of the off-topic question, but merely lack of moderation capabilities. Just because at some point question was able to fly under the radar, that does not mean it should never be moderated.

• An off-topic question hurts the site where it was asked - Off-topic questions hurt the site where they were asked because they provide bad examples of what kind of questions are acceptable. For new users, closed and locked are mostly meaningless banners and those don't stop people from taking such questions as good examples. Often popular off-topic questions are linked in Meta questions asking why was some other similar question closed, when there are others like that highly upvoted and helpful.

• Question needs to be related to the site - While sites have more narrow definition on what constitutes on-topic question than what people may generally perceive as on-topic or site related, when determining the lasting value, question and the answers need to have a strong connection to the site topicality. Completely unrelated question certainly does not represent the lasting value to that site.

• Applicable knowledge - This may be a bit skewed by Stack Overflow perspective. Question must contain some applicable knowledge. In that context—on sites where on-topic implies practical—historical, curiosity satisfying, opinion based, or similar content does not represent any lasting value to the site because there is no practical value you can do something with.

Specific points for off-topic questions that would be on-topic on other SE site(s):

• An off-topic question hurts the site(s) where it would be on-topic - Off-topic questions hurt appropriate target sites because instead of driving traffic to those sites and increasing those sites visibility, they drive traffic to original, off-topic question instead.

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Ideally, we should have the ability to more easily migrate questions regardless of their age, so we could salvage old off-topic questions that would provide good value on another, more appropriate site. Of course, such migration would have to be coordinated between the origin and target site and approved by the moderators on the target site. We don't want to migrate garbage.