You gain many things when you belong to a writing group and develop writing relationships. Confidence in sharing your writing, helpful feedback that guides improvement and mutual encouragement and support. Being around other motivated people when you are having trouble writing helps you stay focused so that you can finish writing your novel.
Love epic fantasy adventure? There's a group for that. Chilling mystery and suspense? There's a group for that too. If there isn't a group already, simply create your own and invite others to join - it's easy.