I think I figured it out... only rarely you'd get immediate interviews, but the idea is you get LinkedIn contacts to chat with later and industry insight, and something to tell recruiters/hiring managers that you did, but you dress it up in a way that shows you look for opportunity like "I met members of [industry/company] at a recruiting conference in [town]". I found industry conferences to be more useful than jobfairs in this respect, but those can be a little to a lot expensive.

Otherwise it's pretty much just being told to scan QR codes, business cards and maybe getting a couple plastic cups and pens.

All in all I say job hunting is such an awful game.