Do you belong to one? Do people in your group discuss their stories in detail, specifically looking for ways to expand them, fill them out? From your own writing experience or from what you’re told by other writers, do such discussions help any individual writer in this particular way?
I belong to one that meets weekly.
We are a pretty close group -- I've hit it off well with all of the regular members. There are occasional members who show up every few weeks, too, and while I don't know them as well, they are all valuable contributors and I trust their opinions. I'm the newest member, and the more established members have told me the horror stories of when the group was first starting out, all the weirdos who joined up and eventually lost interest. It sounds like a writers' group can take a while to mature into a useful critique workshop.
Most of the other members write poetry or essays. I'm the only one who brings prose regularly, though being around so many good poets has inspired me to get into reading and writing poetry, so that's a bonus right there -- a good group will be a safe place for you try out totally new stuff.
We do indeed discuss our weekly pieces in depth. We each read ours aloud while the others follow along silently on their own hard copy, then after reading the writer discusses the piece with each other member of the group. Critiques and suggestions are given, questions are asked about what the writer intended to convey, etc. I've found it very useful, and many of the suggestions they've given me have made my stories and my writing overall much stronger.
I'm very happy to be involved with my group. It's the thing I look forward to most during the week. If you can find a good one with serious, hard-working writers who know the value of criticism, definitely participate! Be aware, though, that you might have to try a few before you find one that works for you. A lot of them, from what I hear, are just attention-seeking wankfests.