It is a explicit representation of a concept we find on many wikis, namely having collections of wiki links to the core pages that allow exploring the wiki content, often found on the starting page. It also makes any IndexingScheme 2-clicks-away if you add a link to SiteNavigation to the header/footer menu.
SiteNavigation differs from MeatBall's IndexingScheme, since the latter talks about general technology of indexing in different engines, while SiteNavigation is a concrete implementation for one wiki engine. While IndexingScheme can serve the purpose on MeatBall, the additional information distracts from using it efficiently, as a MeatBall user. MeatBall's version of this concept is probably StartingPoints.