He includes a code sample that sets up a database object with a custom configuration and calls the "setProfiling" method on it, giving it a value of "TRUE".
This prints out a lovely array with all the queries that have been done. Why is this really useful? Because when using ORM/Model systems the framework builds your queries for you.. This allows you to dig a little deeper, see whats going on, how the queries are being built and were you might need indexes and other changes.