I personally think that for software dev at least, making connections via Twitter or via friends is a better way to go for the first internship, but everyone has different paths to success :)
"Can't risk" is interesting, you could say that about anything you could put on your resume if there's a chance it helps, but something like LinkedIn seems just redundant with your resume's content.
So people definitely use it, even if it isn't on your resume.
If you are going to use it for a job hunt, then use it aggressively. Message/cold-call people that you want to work for, send them a cover letter and CV, ask to talk off LI and on the phone/over-coffee asap. Cold-emailing people from a company directory is kinda the same thing here. The 'rules' for Tinder aren't that far off for LI, sad as that is.
Outside of a job hunt that you're preforming, yeah, it's mostly recruiter spam. The feed is practically useless in my experience, but I am not a power user.
All that said, networking is that key to getting hired.
> Plus every career counselor I've seen has suggested it.
They're probably right, if your goal is to get a job as a career counselor.