Why can I create more than one Master template?

There are multiple reasons to make multiple master templates. Commonly it is used to provide different navigations and styling differences.

You can create multiple Master templates for multiple reasons. 

The most common use case is to apply alternative styling on a different area of your website. 

One example is to offer a full-width and a boxed-width container for your pages. View the 'Creating master templates' tutorial video for more information.