View Controllers - iOS Programming: The Big Nerd Ranch Guide - page 250

View Controller Subclasses and Templates
In this exercise, you created a UIViewController subclass using the NSObject tem-
plate and an empty XIB file. This is useful for learning how the XIB file works. However,
in practice, you typically let Xcode do the grunt work and use the UIViewController
subclass template.
Over the course of this topic, you will create a lot of view controllers. To save on time and
potential errors, you'll use the UIViewController template when a view controller
will have a XIB file. When you create a view controller subclass with a XIB template, the
XIB's File's Owner is already set to the class of that view controller. It also has an instance
of UIView already hooked up to the File's Owner 's view outlet.
There is a drawback, however, to using the view controller template: there is a lot of code
written in the implementation file. It becomes difficult to see what's going on with all of
this extra junk in the file. Therefore, whenever you create a view controller using this tem-
plate, the first thing we'll ask you to do is delete all of the code in the implementation file
between the @implementation and @end directives.