It's not obvious, but the Help Center actually does have (some limited) guidance about when one should and should not comment. While the Help Center's Privileges pages feel a bit like an unused, forgotten card catalog in a library in the age of internet search, they are nonetheless part of the Help Center. The [Comment Everywhere Privilege][1] page has **guidance** on when and when not to comment:

> ##When should I comment?
> You should submit a comment if you want to:

> * Request **clarification** from the author;
> * Leave **constructive criticism** that guides the author in improving the post;
> * Add relevant but **minor or transient information** to a post (e.g. a link to a related question, or an alert to the author that the question has been updated).

> ## When shouldn't I comment?
> Comments are not recommended for any of the following:

> * **Suggesting corrections** that don't fundamentally change the meaning of the post; instead, make or suggest an edit;
> * **Answering a question** or providing an alternate solution to an existing answer; instead, post an actual answer (or edit to expand an existing one);
> * **Compliments** which do not add new information ("+1, great answer!"); instead, up-vote it and pay it forward;
> * **Criticisms** which do not add anything constructive ("-1, see previous comments you scallywag!"); instead, down-vote (and provide or up-vote a better answer if appropriate);
> * **Secondary discussion** or debating a controversial point; please use chat instead;
> * **Discussion of community behavior or site policies**; please use meta instead.

Personally, I don't think much more guidance needs to be made: it is just **guidance** or **recommendation** after all. The guidance works best when the gentle hand of the community members politely ask people to move "answerments" to actual Answers, and the commenter creates a full-fledged Answer.

I'm not sure how much additional guidance should be provided. Over-specifying the cases runs the risk of overcomplicating the situation, and creating extra cover for "but why was my comment deleted when comment X was left alone on question Y" scenarios. Too-specific rules beget rules-lawyering.



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Full disclosure: I have violated all but the "-1, scallywag!" Criticism anti-pattern above, in comments, on multiple occasions. I am not immune from temptation to violate the guidance on occasion. I think it's important to note that the "policy" is more **guidance or recommendation** than dictum. Guidance/recommendation allows the _community_ to steer behavior from _amongst the populace_, rather than be dictated to from on high.

More importantly, it allows for the exceptions to prove the rule:

* Encouraging comments to first-timers. "Hi [new user], welcome to Photo-SE. This is a great answer! I especially liked [point X that you made]." I do this from time to time to hopefully provide some encouragement for a new user. This is contrary to the **Compliments** admonition above, but it serves a short-term use. If I were diligent and vigilant, I'd go back and remove the comment after a few days / weeks.

* Fun. Sometimes, there are some real gems in the comments. Good ol' fashioned (and well-meaning) internet snark sometimes is gold. This is probably the canonical case of comment exceptions that prove the rule. Gems are the most brilliant in the absence of a bunch of shiny junk rocks. They should be allowed to shine.

* Secondary discussion: I have done it many times. If it's apparent that there's going to be a bit of back-and-forth between me and another commenter, I'll actually _actively_ churn out response comments, in order to more quickly trigger the "Please avoid extended discussions in comments; Consider moving this discussion to chat" option. Then I'll move it to chat, and flag the entire discussion chain to be deleted. Win-win.

Note that the first and last points are transitory in nature. They are short-term violation of the guidelines, followed by cleanup. 

  [1]: https://photo.stackexchange.com/help/privileges/comment