All of the above. I joined out of curiosity, like having an opportunity to discuss all kinds of subjects, like being able to offer information and advise others in areas where I have expertise, enjoy being flip and silly at times. I also have the opportunity to interact with people whose lives and life experiences are very different from mine and that can never be anything but a good thing.
I have made good real friends through GN, although I never intended that. Like most people I have never posted a profile or photo of myself and when I fill in questionnaires, I never enter the prize draw to protect my anonymity.
I only access GN when I am on my computer, never on my phone and I do not have a tablet. I do it at any time of the day, and, occasionally, night. It is the perfect procrastinator. I am only on GN now because I ought to be doing something else