A few days ago I posted an answer on this question. After that the original poster deleted it. I undeleted it because it is a terrible idea to delete questions which people have taken the time to answer — the most likely reason for this deletion was cheating on a test or something like that, as far as one could tell, and vandalizing one's own content is reasonably frowned upon.
A couple of days after that, I happened to need myself something similar to what I knew I had written in than answer and I searched for it. It turned out the question has been deleted by other users. I undeleted as I always do when questions on which people have expended effort in writing answers are deleted.
It was deleted again, again by the votes of people.
I honestly cannot imagine what reasons motivate people to delete a question which has an answer. The question is probably not the best question in the history of the site, the answer is surely not the best answer in the history of the site: sure. But what argument a sensible mind can come up with that decides that it is better not to have the question with its answer than to have it is simply beyond me.
I have spent many hours producing answers on this site, as many others have, and the result of our collective effort is a quite amazing amount of extremely useful information. I have often found myself googling things and finding the answers in posts I have myself written already years ago, both here and MathOverflow, and I have gotten quite an extraordinary number of times thanks from people I know and people I don't know for things that I have written here that were useful to them.
Now, if for whatever byzantine reason users are going to begin deleting useful content I for one simply cannot continue producing it and I cannot in good faith suggest —as I systematically do— to other people that they come and answer questions, for I actually cannot be sure that the effort put into doing that will not simply be wasted.
Are we to value the effort people put in producing the content that actually makes this site or not?
It is surprising to me —and actually very sad— that I do not know what the consensus on this question is. I can vividly remember a time when I would have not even imagined the possibility of needing to ask this.
PS: Just to pick an example of another answer of mine (I am entirely sure that there are hundreds of great answers written by many users posted on bad questions throughout the site), should this question be deleted? It is certainly no better in what respects context and what not that the one I linked above —I'd go as far as saying that it is significantly worse, in fact, and I am completely sure that it is well below our standards. That it is an old question has proven not to be a reason for not looking at it with a critical eye, so: should it be deleted? Are we prepared to live with such a low quality question on our site? I'd only ask to be notified by whoever casts the last delete vote on it, so that I can copy the text of my answer and put it somewhere else, for it has been very useful to me since I wrote it.
PS: I got curious. Here are some 1000 questions which should keep us entertained.