Presumably the page at the end of this link will make the action choices available on this site clear. Lacking a clear distinction between actions and audiences - many sites also mix these two major discovery paths in the same navigation list. This confuses visitors, making it more likely that they will not find the outcome they are looking for, even if the site offers it. Visitors return to sites that make it easy for them to fulfill their goals. Not providing a useful site map.
Site maps serve a function similar to that of a table of contents in a linear text document.
If the visitor's goal is not immediately apparent on the home page, the site map is what most visitors will look for next. At least some usability studies show that most visitors prefer to click to a destination rather than search. Many sites do not provide site maps at all. Some of the larger sites provide site maps for their subsites, but not an overall site map. Large sites may need subsite maps, but they also need an overall site map explaining the organization of subsites.