>It is cost free. It prevents people from filing it again. It provides insight into later problems. It provides a place where people can ask and offer advice on working around it. Sometimes an intractable bug becomes more tractable later. It can provide a clue to a later bug report. Sometimes someone new has a brainwave on how to fix it.

I have to disagree at 1) the assertion that it's cost free, and 2) it will prevent people from filling it again

re: 1) - it creates clutter, which at least to some individuals like myself, can be costly in the form of being overwhelming/frustrating/obstructive/etc. YMMV on cost:reward on keeping issues open indefinitely. There are other solutions like filtering, but if everyone is filtering out untouched issues, there's not much difference from closing it.

re: 2) is predicated on issue creators actually searching the entire backlog for a pre-existing issue, which they may or may not find.

I certainly agree that the issue itself should be kept in the tracking system, and continue to be able to be viewed and referenced for the reasons you state. Also consider that issues can be reopened if they were closed in error.