The other day i necrod a nearly 3 year old forumthread with some new information. A few hours later the person from 3 years ago came back and thanked me because the new information helped them. Sometimes nercomancy is good :)

If old discussions have no value, then the forum is topical and shallow. If old discussions have value then they are deep and go beyond today's thought-pablum.

I just learned a whole terminology and subculture based on this comment alone

I am split on this.

If you allow it, then you get eevblog sort of posts where there are 1000+ comments over 5 years in 50 pages that switch topics so regularly that every 2-5 pages should be entirely seperate posts and reading them because of wanting to find information on the title topic is completely useless.

On the other hand, sometimes an issue will become stale and someone will comment with an update or solution to a problem and get chastised for "necroing" and sometimes their comment with a solution deleted.