Apart from ranking and traffic SEO helps to spread business world wide. It also helps in targeting customers who are actually looking for the products which are provided by you.
I agree with rebecca. SEO is only to drive traffic to your site whether its from a search engine a social network.. It dosent matter. So I guess the answer to your question is no SEO is used to drive traffic.
Targeted Traffic
Increase Visibility in search engines
You can get high ROI (Return on Investment)
You can get long term positioning
Cost-effective
Flexibility
Good measurable results