Checking for is_admin() while creating custom post

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While checking the code of a plugin which creates a custom post I am seeing the developer checking if the request is for the backend using is_admin() and then including the file to register the custom post type and custom field .

// Check if admin
if(is_admin()){
	// Load Custom Post Type
	require_once(plugin_dir_path(__FILE__) . '/includes/my-todo-list-cpt.php');

	// Load Custom Fields
	require_once(plugin_dir_path(__FILE__) . '/includes/my-todo-list-fields.php');
} 

All this while I creatingwas create custom posts /fields without using is_admin() without any problem . The custom post/fields do not show in the front end if I do not check using is_admin() . Could you anybody tell me whats the benefit of using is_admin() while creating a custom post ? Is it a normal practise specially in production code to code like above ?