If you are using do-follow sites then you can get back links. If it's no-follow then it derives more traffic to your website.
Forum posting is great for SEO ranking. Because it is a good quality backlink and also bring traffic. That mean both side are good of forum posting.
---Want to learn how to make $3750/m? We will help you MAKE MONEY, we will bring you TRAFFIC. Join me! Your Seven Figure Lifestyle