New Blog Templates – can we make templates over templates without risk?

Hello,

Running P3 plugin I noticed that New Blog Template is apparently in use on a site created months ago with a template http://screencast.com/t/ohyx7KM2FoL

How is this possible? Does any link remains between a template and a site created with a template?

Can I create a template based on another template ? Can I create a template over a template over template without any risks ?

Please note that I had some redirection issues using the plugin (weirfly, after having created a sites with template it was redirecting to the template urls..??)

The explantion on https://premium.wpmudev.org/project/new-blog-template/ is not very clear:

-The site you’ve customized to use as a template is designed solely to be used as a template and not to be used a functioning site.

-Any changes made to a template blog affect any sites created after you’ve made the new changes, it doesn’t affect sites already created.

-DON’T use your main site as a tempate blog!

What can’t we use our main site as template if we want to ? (knowing that template will reflect changes as we make them)

Thank you very much

Regards

Jean-Louis