I'm in one critique group because their focus is speculative fiction. They'll read a bit of everything, but the primary focus of the text has to be spec fic. The feedback Vision Writers give is invaluable in helping me keep the science/fantasy right. They're a friendly group that maintains a serious writing focus. There's a core group of regulars with others dropping in as and when they can. I've been involved with the group since the late 90s so have seen the core group change many times. We organise a retreat once a year for those who can attend.
Another critique group I'm in has a focus on romance. The feedback I receive from them primarily revolves around character development and relationships. It doesn't have to be a romance for the group to read it, but their feedback will always be character-based. Each member of the group has different strengths and foci, so the feedback is always varied and solid. I've been with this small group for years and we've become friends. We also go on retreat every year where we focus more on our writing than critiquing.
After doing the Year of the Edit through QWC several years ago, I got together with some of the others from that program and we formed our own little mini-group. We meet once a month for writing time, followed by lunch and discussion. I'm always amused that after spending a couple of hours sitting silently side-by-side writing, we walk down to the cafe exclaiming how great it is to spend time with each other.
Earlier this year, I did another workshop through QWC - a novelists' bootcamp, an intense program over a weekend. Out of that program has formed my most recent writing group. We meet once a month for writing and discussion time: 45 mins writing, 15 mins discussion. The format has a name but I keep forgetting it. I keep thinking it's Polgaris, but that's not right - we aren't in David Eddings' Belgariad series. Regardless, the format works really well. Last time I went to a meeting, I wrote a scene map for an entire novel in five hours. I'm going to another one today and hope to complete final edits for No Evil Star and write a synopsis.
So that's the selfish part of writing groups - what I can get out of them. It's not the only part, though. I also put a lot into the groups, offering my own critiques of others work, offering support, becoming involved in impromptu plotting brainstorming sessions. I'm there to help others as well.
It's a happy coincidence that every time I help someone else I learn something for myself ... and we're back to selfish reasons! :)