Well, I'm over thirty, so I do remember metered connections and life without a smartphone. The shared computer reason explains it completely, thanks :)
¯\_(ツ)_/¯ I just used to read books before I had mobile data. Never thought of printing out a discussion forum and don't remember anyone else doing so, that's why I was curious.
Sometimes people would post stuff that would be handy to have while away from the computer. In the late 90s, when Brazilian Jiu-Jitsu was taking off, you could find black belts sharing advice on discussion boards (often very detailed). I would print it and take it to practice.
Damn really?? I have stacks and stacks of discussions from forums and various tutorials I printed off while at school to read later on at home. Everything from bind9 configuration to gun building.. On occasion I still pull some out to review.