I have joined for a few breed club matters. I can say that the number of people there that know what they're talking about in terms of breeding and showing is much higher than here.
The fact places can be made private/members only means the breeders are willing to share more information too. Like BYC, Facebook can be a useful tool, and it can also be a means for an invasion of privacy and spewing of nonsense.
For instance, how many APA licensed judges do you know of that are active on BYC? Few to none. I have talked to several on Facebook without having to hunt them down. I am sure for you it is not as important because you know what you're doing already, but for the newbie---me---their knowledge is invaluable.