For most of the life of Bluelight, we used to do prunes every few years. What that means is, we would go through the content in the forum and mark all the threads we wanted to save by bumping the thread (hence, "bump for prune")... that would make it active within the current year, so it would not be eligible for mass deletion, or we'd move them to the PD Archive subforum (where they still existed to read, but you couldn't make new posts), and then everything not moved that hadn't been active within the past year (or maybe 2 years, can't remember), would be mass deleted, gone forever. We did this to save server space, because back in those days, storage was a lot more expensive, and Bluelight had less funds built up.
A few years ago, after the last prune, we made the executive decision to never do another prune, and also do away with the archives, because storage space is cheap now, and due to our partnerships with research organizations and the ads we host for survey/research study participants, we no longer worry about not having enough money.
But we lost so much stuff because of those prunes.

A ton of random threads by noobs asking basic questions, sure, but also great stuff that nobody bumped for the prune. Some old PD Social threads were lost and lots of threads containing some really great conversation by really good and knowledgeable posters. Fortunately, I was always able to convince the admins that we needed to save every single thread in Trip Reports, no matter what, which is good, because we have the second oldest and second largest repository of trip reports that exists, to my knowledge.
But yeah, no more prunes, ever!