Strengthening the home page with inbound branded links, and mixed commercialized / brand links from editorial / high quality sources builds authority, which as Perfect007 mentioned, distributes 'weight' throughout the website.
This improved domain authority tends to move relevant associated topics within the website up in rankings more than non-related areas. For example, the more tightly knit the homepage is to the categories that comprise it, the more inbound link building to the homepage impacts those pages.
At the same time, link building to strategic inner pages moves the needle as well, and reinforces authority to associated related sub categories and 'sister' categories in the website.
As a basic rule of thumb, competition being equal - the further apart your inner categories are insofar as relations, the more authority you need to build at the base level (root, homepage) in order to move inner categories forward.
Hope this helps.