For me LinkedIn is something I use when I search for a job. Actually it is something I update, because I believe HR will crossreference my resume with my LinkedIn. When I'm not looking for a job, I'm not using it.

The other use case I know is collecting leads (sales or headhunting)

Networking with people who want to do business? Reach out into my network to ask people for help? I have done this a lot on Facebook (a lot more on phone or email), but never on LinkedIn.

They could have build the next slack or something. A platform where people communicate.