Barbara Thomas at 2013-04-09 14:56:46:
I belong to the North Richardson Screenwriters Group (serving the Dallas area). We meet every other Monday.
For me, the benefits are:
Community: Writing can be very lonely work. It's nice to get out of the house, talk to people who are in your same boat and will celebrate your little victories and sympathize with your rejections.
Goal-setting: I always want to have new pages to bring to a meeting so I always push myself to have ten pages done every two weeks.
Brainstorming: Sometimes a member will come to the group with an idea or a logline or a sticky plot point and we talk it out, each person building off the other's ideas.
You can get much of the same benefits from an online group, I suppose. But I like being able to talk to warm bodies once in a while.