Been on the site for 14 years.
It serves no purpose other than shameless hot air and self-promotion, interspersed with ads and corporate marketing bullshit.
When I joined, it was simply an IT industry oriented networking site. Obviously that has scaled and morphed.
I get all kinds of inane recruiter-bs and I politely decline, or simply delete depending on content.
I never made any effort to 'expand' my contacts. But all of my contacts are legitimate and I know them personally, unlike most users.
With the correct applied scrutiny, you can make it work for you, but it's relevance in todays Interwebs of Everything is sinking.
I wouldn't say it's a bottom-feeding social media site like Farcebook, but it's probably one rung above.... certainly not buoyant with enriching content.
If you're not in the IT-related industry, I'd say do not bother with it.