If you are using a 3rd plugin such as: WooCommerce Subscription; WooCommerce Product Vendors … and the email contents of this 3rd plugin is not attached in WooCommerce default emails, but they create their own email templates. In this case, you can use the default template type.
This template can help to keep the email form of the email template plugin including the header, footer, suggested products and socials, and load all email contents of the 3rd plugin inside.
All email contents of the 3rd plugin will keep it initial format and can not be customized by WooCommerce Email Template Customizer plugin.
For example, you are using WooCommerce Product Vendors and want to show all email contents of this plugin. You can see the default email template can load the contents of WooCommerce Product Vendors and also display core design of WooCommerce Email Template Customizer:
