What is a ... base?  

Overview

You should think of a base as a connector in your configuration in site explorer. It allows you to subdivide your site into sections to make for more logical navigation. In the same way that we group related files in the same folder in Windows Explorer, we can group related web pages in the same base site in site explorer. 

Look at the example configuration here. We'll see a number of base sites in this configuration including church, GAA, Business, Education & Further Education (contained in Education). Applying this configuration makes a lot of sense to avoid cluttering our main menu. We can drill down to categories and sub categories within a topic without causing confusion.

Imagine we are setting up a community portal website. There are a number of local organisations interested in publishing content on our site including schools, church, soccer club, drama society, golf club, historical society, businesses, tourism board, athletics club etc. Straight away we can see certain synergies & relationships between some of the organistaions so we could group the soccer club, golf club & athletics club into a single category - sport. This category would then branch off into the 3 different sports. Likewise we could group historical soceity, businesses & tourism board together into attractions. This makes a lot of sense for larger sites as the final site will look far more structured and less cluttered.

As a second example, lets say we are setting up a website for a supermarket and we want to advertise our stock. It would make sense to subdivide the menu into relavent sections so we could put all the food together, all the hardware together, all the drapery together & all the household items together etc. We can then subdivide the food section further into vegtables, meat , fruit etc. 

If you have a website with less than 7 or 8 pages, there probably is no need to use a base site. If it goes over this however, it may be worth using.