Similar to the rating system, but if the post/answer is negative then the topic creator can choose to hide the comment.
I have just received an answer for one of my questions and the person has just pretty told a joke and posted nothing which would help me in the slightest.
So if I could hide the comment (only to show if people are really curious) it would help anyone else who has a similar question to mine and doesn't want any junk posts.
Obviously this rule won't work in Chatterbank but may be useful to other topics.
That would presume you own and control the thread, and that could never be allowed to happen (I think). I suppose if abusers of the system were to remove undesirable comments, or undesirable ABers from their threads, then there is a risk that people would probably just stop answering you.