Moderators have long had access to a tool for converting answers into comments. The guidance for this tool reads as follows:
Answers should be converted to comments when they contain useful information, but do not answer the question.
This sets some pretty lenient requirements for the use of the feature; strictly-speaking, you could convert any answer that didn't successfully solve the asker's problem to a comment without violating it. This probably wasn't the intended goal, but (sad to say) I've more than once seen it used as a rep-denial mechanism for lazy-looking answers that no-one felt like downvoting. This just ain't right... And it's our fault for providing crappy guidance to new moderators.
The Not an Answer flag once had this problem as well, which we attempted to address by tweaking the wording slightly. Subsequent hairsplitting aside, I tend to think this has at least made life less confusing for the more engaged users (and moderators, who - with sufficient hair-splitting - have an easy-to-defend reason for declining flags on answers that someone just doesn't want to downvote). I think it's high time to remove the ambiguity for Convert to Comment as well.
Here's my revised guidance:
Answers should be converted to comments when they do not attempt to answer the question, but do provide useful information or requests for clarification pertinent to another post.
My rationale for this change is that "convert to comment" is most useful and least abusive when it is used to preserve comments from users who do not have the reputation to comment, and so post their (useful) comments as answers. It is not meant as a way to convert useless answers into useless comments, or deny reputation from useful answers. Therefore, the guidance should clearly state the requirement that a given post make no attempt to provide an answer, and also make note of the sorts of comments worth preserving (errata).
Anyone have any objections to this change (or improvements to my wording)?