Some ways in whihc social bookmarking help:
* Promotion Tool - Firstly, we (SEO/Webmasters) have got an another free, simple and advanced tool to promote web pages.
* Easy and Fast Indexing - Generally, all social bookmarking sites have good traffic and fast search engine indexing. So, if we submit our URL / web page in a website which continuously crawled by Search engines, we can also get easy and fast indexing for our websites.
* Extra Traffic - Many social bookmarking services provide web feeds for their lists of bookmarks, including lists organized by tags. This allows subscribers to become aware of new bookmarks as they are saved, shared, and tagged by other users. By this, site can get more traffic from the web.
* Web Popularity - If your post or bookmark is useful to other members, then surely they will also bookmark it and will you get extra point to your bookmark. All Social bookmarking websites have this process of voting. More and more votes you get, more popularity you will gain for the web page.