New Style.css Practice

I am seeing more and more Wordpress themes call two stylesheets:

1) the standard style.css file in the root of the theme folder. This is required by Wordpress.
2) A second file in css/style.css

However, the standard style.css file is left empty with usually just the following:

Theme Name: The Theme
Theme URI:
Description: The theme.
Author: Joe
Version: 1.0
/* please see css/styles.css */

What are the advantages of keeping the main style.css empty and copying all styles into a separate file at css/style.css? I have noticed this practice becoming more and more common so there must be a reason. Any ideas?