Social bookmarking software allows you to place a bookmark on many social bookmarking sites in the same time that it would take you to create a single bookmark manually. It allows you to do so much more than you could feasibly do manually due to time constraints.
There are two primary ways in which social bookmarking can help you promote your website content and that is 1) by giving you backlinks and 2) by sending you traffic. Although you can do this manually without the help of software, the time needed is quite high and the work can be rather tedious. If you use fully automated software that handles the submission process for you on auto-pilot then this becomes a very effective method of promotion for very little time investment!
Every bookmark you place at a social bookmarking site gives you one backlink to the page you are bookmarking. Therefore it follows that the more sites you can bookmark at, the more backlinks you get for each piece of content. This is the primary reason why social bookmarking software it so useful because it simply multiplies your efforts for the same amount of time invested.
However there is one thing to look out for - some software tools will submit those bookmarks all in one go which is not ideal. Search engines such as Google give more credit to backlinks when they come in on a regular basis over time rather than when there is a sudden surge of them. In the latter case some of the links will be ignored. Choose a tool such as IMAutomator which will spread those links out for you over a number of days.
The second way in which social bookmarking can help with website promotion is traffic. The reason these bookmarks are 'social' is because they are shared by the community of the bookmarking site. The way in which most of these sites work is that they allow members to post links that may be of interest to other members but the members also have the ability to vote for particular bookmarks that they like. Popular bookmarks usually get special attention such as appearing on the home page of the site.
This offers a number of benefits. To start with, the home page of the site will often have a higher page rank than other pages which means that the backlink is stronger while it stays there. The biggest advantage however is visibility - members see the home page and therefore the most popular bookmarks before any others and so it follows that those bookmarks get far more traffic than the rest.
Some social bookmarking sites are now so popular that they get literally millions of visitors every day. Digg, for example, is one such site. Getting your bookmark onto the front page of Digg is most definitely something to aim for as it will drive thousands of visitors to your site! Not only that... but there are now aggregator websites such as PopUrls which trawls all the big bookmarking sites for their popular links of the day and re-posts them - this means that you're now getting extra backlinks and extra traffic!
For maximum effectiveness get into the habit of bookmarking all of your best content on a regular basis. There's no need to do this manually as you can use a free social bookmarking software tool to do the hard work for you! Just spend a couple of minutes every day to receive a constant stream of traffic and backlinks to your pages!