Both

In my personal point of view, I enjoy groups because they are places to go for individuals with certain interests. For example photography allows people to go there to see what people of similar interest are doing. I am an ex-JW so the JW group is of special interest to me. I don't see this dividing anyone but if we think about it, I would imagine that a majority of people on agnostic.com are here because we want to be able to share thoughts with like minded individuals without as much fear of being constantly attacked for our views. So if folks have right or left leading groups it's about the same thing.

I think they help narrow down the 45,000 members into something manageable.
I just wish some groups actually were what their titles imply they are and they would limit posts to the topic.

The ones I am in, especially the music groups are great. I have been exposed to new music daily, some I wouldn’t choose to listen to, but most are expanding my knowledge and appreciation of diverse music.

I’ve had the same concern, or question, thus have not joined any… I love photography, for example, but am not going to ‘join’ a specific group of the same; place it on the main board - and let’s all enjoy and/ or contribute.

I envision other groups as merely eco chambers, with bored occupants occasionally attempting to provoke those outside to join up for a fight. No thanks