I believe that this should be determined on a case by case basis by considering what would be the most useful to future readers of the site. 

If the question is on topic, I don't see the benefit of editing it to make it off-topic. I've seen the reverse encouraged [here](https://askubuntu.com/help/closed-questions) "it may be necessary to reword the question to fit this site's scope after reviewing the community guidelines." but have yet to see anything to indicate that a post should be edited to make it off topic.