If a thread shouldn't be bumped then ideally it would be closed or archived, but BL has an organic flow about such things. Usually threads just move to dormant on their own without mods needing to lock them or do anything.
There are some bumping of threads that doesn't make any sense to me though. Say someone had a thread about going the possibility of going to jail in 2007, the last post is 2007 sometime. Then someone posts in that thread to give them advice in 2010. I've seen stuff like that and just been wtf? and mods tend to post some sort of polite wtf? comment and lock the thread.
Some subjects are specifically supposed to happen in certain threads by forum guidelines. The
price threadd in OD being one example. TDS guidelines mention that posting in megathreads or starting your own thread is entirely to be decided by what you are comfortable with. It is encouraged to use the search function before posting, especially with subjects that are likely to already have a thread with all the info you want.
So reading individual forum guidelines and using common sense about what sorts of bumps of old treads might increase efficiency or diminish it. If you need data and the most recent thread on the subject is several years old with no activity, it is a good bet no one will be upset about your starting a new thread. Reasons for preferring people not start new threads are that the topic comes up quite a bit and organization and efficiency makes it better to be all in one place. A comprehensive thread gets all the data in one place for members consideration instead of a snippet here and a factoid there.