I have been on a few horse related ones over the years, primarily a regional riders one which was my social and riding company when I was working and all my nonwork hours were taken up with riding, breeding and horse care. Then a UK wide version of it, which kept me in chat and horsey talk - both relatively small closed groups. I left both when I was no longer riding and had little to contribute to the discussions any more.
I've also been on two consecutive Highland pony specific ones - the first one started free but began to close ranks and in 2007 insisted it was for paid members use only so I left as it felt like a membership fee exercise and a bit manipulative. As did several others, some of whom then began their own free list to replace it so I joined that and have been there ever since. In all cases these were to discuss things I couldn't discuss in my everyday life in an office, keep in touch with other breeders and keep up to date with the HP world as I no longer show or ride so don't meet the people in person much any more.
TAS I joined when I left work and went full time here, I think. For specific information and to feel a little less alone in my lifestyle choices. I rarely leave the holding now, a weekly trip to the local library and supermarket, the GP etc but other than that not much. And socially I thus have very little to say to anyone not interested in days spent weeding or moving ponies from field A to field B in sequence to keep the stallion from nonbreeding mares, or worrying about hens or silvery tinge coming over plum leaves or whether this piece of fencing is higher priority or best done before that bit of field drainage repair, or when to plant willow or whatever it is I have as a potential topic of conversation. I don't watch soaps or read newspapers or care about celebs or fashion so I'm just not that interesting out there!
So if I didn't talk online I wouldn't really have anyone or anywhere else. I've one neighbour, a couple, and a few acquaintances locally I can pass time with occasionally but I can't afford to get too involved in their social lives, even if we had anything much in common to discuss. Rounds of golf, holidays in Spain or taking turns with dinner parties in houses that actually have a dining table perhaps? Hmm, no thanks, the one about what kind of wellies or how to worm hens is more in my comfort zone to talk about!