User class can be saved to the database, but it's also a normal Ruby class, too. Accordingly, you can add methods to it to give yourself functionality that might be a pain to get with a SQL statement.
For example, some users will enter only their first name or only their last name, or no name at all. It'd be convenient to have a method that accounts for this, so:
require 'tutorial_setup' class User < Lafcadio::DomainObject def name; [ first_name, last_name ].compact.join( ' ' ); end end