…is that they should be in some way related to the post they’re attached to. I delete comments that have no relation to the post, especially if they’re advertising something (even if what’s being advertised is worthwhile).
That’s why I recently deleted a comment that was awaiting moderation. It had nothing to do with the post it was attached to.
Nonetheless, it pointed to a YouTube clip (in Spanish, with English subtitles) that I enjoyed, so I’ll provide the link myself: