Conferences are like huge weddings. People have convened for a common purpose of course (of presenting their work), all very well-dressed and all, but everyone has their own side agenda going on.
For some, it is a reunion- Old buddies meet up, hug, hang out, have drinks and meals, discuss their research, catch up, and make such a lively crowd. They are usually the ones much older and well-settled in their careers, the associate professors and the full professors, or the ones with permanent positions. They are done with the arduous task of looking for a job or getting tenure. They are dressed less formally and hang out in larger groups.
For some, it is getting away from work, only to get some more work done. They usually sit at the corners with their laptops, poring over their data and typing furiously. They are like little isolated islands. They are the ones with approaching tenures or appraisals.
For some, it is about networking and job hunting- Finding employers and employees. They sit in smaller groups and talk more seriously. Usually, one person is older and more mature and talks the most, while the other one is much younger and looks in wide-eyed appreciation. They are usually found in smaller groups of twos and threes, the younger one dressed very formally. They are the postdocs and the ones still looking for next year's job.
For some, it is about finding collaborators. They talk more seriously, in groups of twos, moving their hands frantically. They say goodbyes with promises of sharing research proposals, attending one another's talks, and finding each other on LinkedIn. They are the ones about to start something totally new.
For some, it is all about their talk. They look visibly nervous, fixing their slides until the last moment. They don't understand that it is really informal, and people have come here to enjoy themselves, academically speaking. They are usually the younger graduate students.
I suspect that there is also a small group of people who have been set up, trying to find dates and mates (although that was not the primary intent). They are usually the ones making awkward conversation.
And for me, I am just happy to sit back and watch human behavior- how people talk and walk and dress, meet some old friends and colleagues, disappear for a couple of hours to get some work done, support close friends by going to their presentations, get a little nervous at my own presentation, and above all, just take in the sights and smells of a new city.
P.S.: Ever seen how everyone walks very fast at conferences? I have seldom seen anyone walking slowly or looking lost.