To use parent template for child categories or pages. This plugin patches template hierarchy. This plugin is for who create or customize themes.
If you have works category with some child categories as followings, you may want to use 'category-works.php' for all three child categories. You need to copy as 'category-design.php' and the rest in default template hierarchy. WP Use parent template patches the template hierarchy to use parent template for these child categories. And also pages too.
See following for WordPress default template hierarchy. http://codex.wordpress.org/Template_Hierarchy