As an author, you need support. You need honest feedback. You may even need help figuring out certain writing techniques and double-checking your ideas. It's attractive to start joining guilds and groups, and plenty of writers advocate that. But when you mix with other people, you're always going to wind up with a mixed bag. Joining groups and getting involved has a good side...but plenty of writers will tell you about that. I'm going to flip the coin, and talk about the dark side of sharing your writing with other people before you've finished with it.
Team Players
I have often mentioned my childhood fantasy of being a writer. I would be sitting in a quiet room -- maybe in an attic, somewhere, or some book-lined room -- all alone just typing away. That, to me, is truly living the dream. Why? Because writing is solitary. You do it alone. To me, the idea of joining up with other writers has always seemed...damned counter-productive, to put it mildly.
But even I can see the merits in it. Writer groups can be helpful if you've got questions or want to test your ideas. Joining a group can help you find beta readers and review buddies and, I guess, lifelong friends.