I have often seen our moderators leave detailed and helpful comments, usually to new users. Some examples from the front page right now:
Hi and welcome to Literature Stack Exchange. I have noticed that somebody has downvoted your question and that is not a pleasant first experience. The reason was presumably that the question does not show enough effort (it is, after all, very short). You can considerably improve the question by adding what you already know (including what we supposed "all know (about) the differences between Antony and Brutus). See also How do I ask a good question? in the Help Centre. Good luck! – Tsundoku♦ 25 mins ago
Hi. Since you have been on the Stack Exchange network, I assume you know that the rules are against questions that invite strongly opinion-based answers. (See e.g. What types of questions should I avoid asking?) For this reason, I would appreciate it if you could edit your question to clarify how people should answer your question without relying solely on personal opinions. – Tsundoku♦ 3 hours ago
Hi and welcome to Literature Stack Exchange. This site has different rules than a forum, so I would recommend that you take the tour and review at least How do I write a good answer? in the Help Centre. For example, answers should really attempt to provide an answer to the question instead of commenting on it. As it currently stands, your answer consist for a large part of speculation ("I suspect, ...") and a recommendation for the Audible version, which is not relevant to the question. – Tsundoku♦ 7 hours ago
Is there a list of comment templates that I could use along the lines above? If not, would it be useful to compile and curate such a list?
Of course, it's not possible to cover every possible scenario, and it would be better to always tweak any template to suit a particular situation, but comments like the above are (in my opinion) useful in guiding new users to ask better questions and write better answers. Leaving such comments would also be a more active form of feedback compared to just voting and flagging.