Such groups are indeed helpful especially if you hit a dead end but I think one shouldn't rely too much on it. I believe if you don't know what you should write or research, it's better to ask your supervisor since he or she knows more than the people in such groups. Still, probably attending such meetings won't help you with writing your own paper but it may show your a way to how do it. And as pointed out by the Writing Center at UNC-Chapel Hill writing a dissertation is a transition from a student to a scholar and it turns out to be stressful. And with this groups will help you. Additionally, the blog from DW mentions you should be able to distinguish between a simple research paper and a dissertation. Simply put before writing it, you should know how it should look and what it should contain. These answers you will find when consulting with your supervisor.