Javascript - Spine MVC - Class

I searched all of StackOverflow, but I could not find an answer for this.

What is the purpose of a class in Spine (MVC Javascript Framework)? http://maccman.github.com/spine/#h-classes

I mean ... I read the docs, but it seems like I can't imagine an example of the real world to use Classes, and every time I think of something that is likely to be right for him, I understand that I just confuse it with the Model.

Will someone be kind enough to explain to me where it would be convenient to use Spline.Class?

Thank.