Students come and spend days in a happy daze, meeting the oldtimers whose papers they've been studying and getting a wild surmise of the possibilities for their own lives. Many undergraduates present their senior theses here, an experience that can't be gained any other way. Their wide-eyed presence makes everyone else happier. In fact, even local high-schoolers are here too, reminding me of the thrill of attending the GSA meeting as a teen in 1968. That was a special time in the history of geology, but you know, these days geology is still in a golden age.
I shouldn't leave out the commercial companies and agencies that exhibit here, making valuable contacts with their clients and customers. They show up at the talks, too. And they hand out some cool schwag, too. There's a whole ecosystem that assembles for a major scientific meeting, and the people who are "in the life" treasure the good ones.