It's a professional social network. For example, I just had an acquaintance message me via linkedin, send me their resume which then let me refer them, getting them a job and myself a nice bonus.

Could it have been done via Facebook or email? Maybe, but we're not social friends, so no Facebook connections between us, and we don't know each other's email addresses so they couldn't have discovered me easily.

The semantics of linkedin are what matters. It's not a social network that's highly interactive in the way that email or facebook is, it's more an on-line resume post + people you've worked with that help establish the milieu you live in.

Does linkedin "get" it? I dunno. I suspect that they do, but their growth targets can't accept this, so they keep doing things weirdly.

Linkedin is a lead generation machine. You can outreach pretty much anybody from any industry. People are usually open and as long as you don't spam them, you can start conversation with anybody and showcase your expertise. I have an account for 10 years and only last year I saw the value of it. I used to get a lot of spam and job offers from recruiters, but it has going down. Also, I recommend creating an email just for it because as soon as you add people they can see your email address.

Mostly it's a reverse job-board: "Here are my skills, work history, and list of people you may know that are willing to say that I rock; call me if you want to hire me." The farther along and more successful you are in your career, the better the offers you get are. It has secondary functions like keeping track of people in your network and some social media aspects (that hardly anyone uses) but that's the primary one.

LinkedIn is for professional networking. If Facebook had the equivalent of Google+'s circles to segment your friend list by type, LinkedIn would be unnecessary. But since they don't, LinkedIn keeps me connected to people that I don't want seeing my personal updates and people that I need to contact when looking for work or trying to fill an opening I feel is high quality.

All the posts and reminders are worthless to me and only serve to annoy me. It's the professional graph and messaging that I find valuable.

As a student it helps me research companies by meeting and talking to actual people outside of an office environment. It allows me to ask people for favours which a lot of people are more than happy to do.

Keeping in touch with professionals also helps me keep the slight acquaintance going so that I can hit them up for a favour later.

I get a lot more emails after creating an account. Makes me feel kind of popular I guess.