Deep link building are used to increase the traffic for the inner pages and it can also help to increase link popularity but its very hard to achieve one.

Deep linking gets better your site/blog usability and
Deep linking optimizes every page of your site.

Deep link SEO is more depend on the url structure and relevant URL name. When addressing inner pages URL, do not use '-' as a separator in stand of '_'. Keyword density should be maintained in content of website as well as Meta tags.