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Some threads you might want to keep open depending on the subject while others should be closed.
 
Software could lock threads automatically, but it takes human judgment to know if a thread should be locked. Sometimes old threads are still useful. In cases where someone has a new question about an old issue, an old thread can even provide more context than a brand new thread would.

Do thread resurrections cause a problem for you?
 
Maybe we just need threads to fade and get smaller, as they age! Then again, if somebody does a forum search and finds an old thread, it was likely one of the top hits for the search terms they used.

It might be interesting to study a few such cases and try to figure out how they happened upon that particular old thread.
 
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