Surprised to see LinkedIn's 930 million MAU! I might have heard someone mention it irl like 2 times my whole life? But maybe that's cuz I'm not in the job market yet.
It has different aspects to it. Big part of it is job hunters i believe, but i use it mostly for promotion of my research, discussion with other researchers, policy discussions and following conferences / webinars and news about climate related stuff. I use it daily.
Like most popular social media sites, you usually won't see very valuable discussion in the comments, at least in my experience. It's mostly for people to post news, research, and so on, and follow the big names or organizations in their field.
Most of the valuable information is diffused via posts but I do put a bit of time and effort into trying to filter out all the crap posts like memes, the faux inspirational stuff, self-aggrandizing nonsense, etc.
It's big for sales people too - I research who is the right person to contact at an organization, and also to find out what they've been up to lately that might be useful in a sales pitch.