After college, my reddit was mostly used to keep up with product reviews (especially in terms of durability), tech news, and biomed research, and a lot of times I got guidance on hyperspecific issues from a lot of the professionals in those communities.
Also have to give a huge shoutout to r/resumes and the other large jobhunting subreddits-- I don't think I'd have found a job at all if it weren't for their megathreads and resources