Well, I don't know why he did this, what was his reason or so; it is simply his decision to delete his answer. But actually he didn't delete it rather cited the reason 'in order to comply to the site policy'.
Can anyone please explain which site policy did compel him to partially delete many of his answers?
It is the very difficult policies on homework-like questions.
What is Stack? What is PSE?
The Stack system is a dynamic community FAQ which works by a combination of the psychological "rush" of earning points (even if those points are, so to speak, pointless), community reviews of popular questions, and having an unusually low impedance for both questions and answers. Traditionally a FAQ grows by a community finally getting upset that the same questions get asked so many times of its members, and someone rises to the occasion to create one document which others can link. The biggest curiosity in all of this is that the causality is flipped from "community nuisance → FAQ" to "FAQ → community nuisance," as the community in question does not actually exist for any other reason than to participate in the making of the FAQ.
Physics has three properties, at least, which complicate this mission:
- It is deeply technical. Physics tersely summarizes the world in a specialized language which takes years to speak fluently.
- It is intrinsically popular, or maybe "popularizable" is a better term. It is popular in the sense that translations of its terse summaries are deeply interesting to people who do not speak the language.
- It is required. Everybody in a civilized society is expected to learn some of the basics of the language and some of the most common idioms.
Note that Stack Overflow, which the Stack system was designed for, only has about half of property (1) to deal with, and none of properties (2) or (3).
Due to these, there are generally fewer qualified answerers than askers, and a lot of questions which are fundamentally the same (they depend on the same grammar error in different sentences) appear as very different-sounding questions with no easy way to mark them as "duplicates" of each other. Furthermore, we get a lot of 'pop-sci' questions which cannot easily be answered, as well as a lot of homework questions from a lot of unspecified textbooks.
Stack is not a very suitable match for the latter two, and degenerates essentially into Yahoo! Answers: one-on-one tutoring that may potentially be seen by some other people, but is not long-term in the way that a FAQ is meant to be long-term.
Furthermore, though it is hard to measure, it means that our
(qualified answerer)/asker ratio at any given skill-level is much lower than that for Stack Overflow. This makes qualified answerers a rarer commodity, and more precious. Probably it should be a community goal to make people who can answer the tough questions feel like royalty; I would hope at least that people like Emilio Pisanty (just as an example, I could write several paragraphs of names that I respect here!) know that people like me look up to them.
What are the policies and why do they complicate things for answerers?
There are two basic homework policies: first off, we close homework-like questions for not "putting some thought into it"; this is a way of simply setting a floor of minimum competency-with-the-language before allowing a question to be asked, trying to improve the ratio. (We might want to consider a similar policy for pop-science posts!). Usually this doesn't disturb the answerers, though if they've already written out a good answer it may rob them of a +15-point psychological reward.
Second, we sometimes delete answers to homework-like questions for getting too close to the answer. This is unbelievably irritating. Like, even if you know why this policy exists (to further discourage those homework questions, and to get qualified answerers to spend more time on meatier questions), it still takes the form of telling our qualified answerers "you did something wrong!" and it is probably what induced the above rage-quit.
It caused me to rage-quit for a while when I was starting out, too. Fundamentally it says "that hour you poured into this question has hereby been wasted by administrative vote."
The first problem with this policy is that it is intrinsically vague, which is probably why the user in question just started deleting everything. He writes (wrote?) lots of very visual, long, comprehensive answers: and if he poured several hours into a post which was then deleted, essentially because he poured too much time into it, it's no wonder that he goes back to everything that he's poured a lot of time into, editing them all to say "Hey, apparently I spent too much time on this which means that rather than editing down the answer, site policy requires us to delete it all."
I think the other big problem for me is that I feel disrespected as a volunteer when this happens. I feel like it is my right to make the choice up-front of "I'm going to pour some time into this," a right that is only taken away by closing the question before I get to it. By deleting my answer after I've already sunk my time into it moderators are effectively saying "your voluntary effort here was garbage." It's very tempting to respond to those feelings of disrespect with a, "that's fine, I'll just volunteer somewhere else where people actually respect my contributions."
So, I have had no involvement in this particular user's case, but that's my first thought of why the user would think that all of their contributions were illegal according to site policy: it's that they were if you judge the vague policy broadly enough, and probably they were upset that it was being judged just broadly enough to delete something that he'd poured several hours of his time into.