[ImpactBreaker]

Just use good sense. Some thread have clearly died out, when you think about reviving the thread you have to read every post carefully sometimes a question that was made in the thread has already been answered and there's no need to repeat it all over or even worse, ask the same question (that has already been answered in the thread) again just because you didn't read it carefully.
Other threads could actually be discussed for eternity though and reviving them when you feel like discussing isn't really a problem in my opinion. You just have to use the good sense whether an old thread would still be interesting to still be discussed or not.