Occasionally, I write a comment about an answer or question; then the author makes an edit, telling me "@einpoklum: see edit" or something similar. At this point, and if my comment is not otherwise relevant, I delete it, and flag the author's comment as "no longer needed". But really, I don't want to bother moderators with this task; I actually want to just tell the author s/he can remove the comment. Now, I could do that with another comment of mine, but that would kind of defeat the point.
I wish there could be a "tell author this is no longer needed"-type flagging option.