Ah sure, easy one. Here’s an example taken from literally the most recent QA I visited on Stack Overflow, from my history:
Now, the first sentence is obviously obsolete, as the answer was indeed accepted. The comment is overall useful and should be visible just the way it is, though (IMO), since it not only states “this should be the accepted answer”, but also explains exactly why. Does that information belong in another answer? I’d say no. Does it belong in a discussion page? I don’t think so either.
Another example from this answer:
… now also obsolete because it was incorporated to the answer. But before it was… It was useful and should not be hidden under a ‘Discussions’ tab.
This comment is just a great complement to what is already a great answer. If the author of the answer wants to add that info to their text, great. If not… I’d like to have this comment visible right under the answer so we can benefit from it.