Make sure you have links coming in to as many pages as possible. What does it tell a search engine when other web sites are linking to different pages on your site? That you obviously have lots of worthwhile content. What does it tell a search engine that all your links are coming in to the home page? That you have a shallow site of little value, or that your links were generated by automation rather than by the value of your site. Here is an example of deep linking, in this case to my personal happiness workbook.
Re: Deep linking is very useful
As addition to deep linking, if you are optimizing a certain keywords for specific page of your site, deep linking or page targeting take place. Sometimes, its necessary to create an individual page for every keywords and create a good content exclusively for that term to make it easier for you to rank your keywords.