Social bookmarking is a method for Internet users to share, organize, search, and manage bookmarks of web resources. Social bookmarking helps to improve the ranking, traffic and also helps in quick indexing. It is good if we submit in dofollow social bookmarking it helps to pass link juice.
Social bookmarking tends to help SEO indirectly as most of the commonly used social sites such as twitter and digg are all no followed. the positive effects from an SEO side of things are the links attained by gettin your content in front of people.