I love my ukes! It's not uncommon for people to become very fond of their favorite uke brands/makers, so why not share this with others like you? The groups also provide a good place to get advice on what strings and things that others like to use on the same instrument you have.
And just because I have a Kamaka doesn't mean I don't want a KoAloha or a Kanile'a. The goal is to join as many groups as possible by accumulating as many ukes as possible!
Necessary? Is an entire website devoted to ukulele discussion, education, and enjoyment necessary? Is anything we do to pass away the time necessary? Should we fast forward from being born to being dead? Really what's the point in anything?
I think it's a great way to find out why people like a brand. These folks are so helpful and friendly, that they will answer all kinds of questions to help you make your decision. And, if you take a look at the list of ukes people share, it is usually a mix bag of brands and sizes. That's half the fun after all. So most people could belong happily to several groups.
No, and it doesn't really do anything for me either, but hey, no foul. I just ignore those threads, and post on the lots and lots and lots that DO do something for me. I suggest you join me. We can call ourselves "The clubless club"