So we know about which questions have insufficient answers.
Or, of course, have all question that have '(Unresolved)' in the title also appear in the Unanswered list. But you get it.
In the Unanswered list there are options to view "no selected answer" and "no upvoted answer". That should cover most circumstances.
I do have an idea for an official way to mark things as "unresolved" but it will probably be a long time before I get round to adding it.