For me, it’s a few things.
- 
A way to burn time that doesn’t feel like a digital sugar rush. 
- 
Support, camaraderie, and kindness, primarily from /r/stopdrinking. 
- 
Niche stuff, like ideas for local hiking and backpacking trips, propaganda posters, and kayaking info. 


Hobbies are really the thing. And a source for funny videos. I don’t need the big subreddits for politics and news, much as I tend to get sucked into them, but I do really like having a wide range of subforums for my niche interests. It’s much easier to find someone to talk to about a small tabletop RPG on a large aggregate site than it is to search for sufficiently active independent forums.