It's how people talk to groups of dozens of people at a time: friends, neighbors, acquaintances, the parents of your kid's school mates to discuss school stuff or to setup a birthday party… coworkers if you include more work oriented chat apps.
I have dozens of such groups, some with photos of kids around a birthday cake that I'd never have put up of Facebook (if I still used it).
If that's not social networking, I'm not sure what is.