From a recent post in "General."
The reviving of old dead threads - and newbies or folks who may not be aware that a thread is old; and
the possibility of some sort of screen warning coming up when someone posts to a "dead" thread - such as:
"You are posting to a thread that has had no activity for 12 months" - or something like that.
It doesn't prevent folks from posting, just gives them a clue that perhaps a new thread is in order, as it is likely that the original posters are no longer on the forum, or may have even changed their positions on the topic.