I really like the fact that closing a question as a duplicate, or with the custom off-topic reason, auto-generates a comment.
This auto-comment often generates a discussion about the question, that helps educate the close-voters, the original poster, and the rest of the community about the topicality of the question. Many times, someone replies to the comment, and the votes on both comments indicate what the community thinks should happen.
Here is one example:
Add an auto-generated comment for all close votes, regardless of the close reason. If another close-voter selects the same reason, the auto-comment should be upvoted.
This thread feature request Auto add comment on close vote is related, but that one emphasizes notifying the OP that their question is about to get closed. This request is different, because it emphasises educating the community1 about the topicality of questions, and also as a mechanism to achieve consensus.