There is a huge difference between “RW normal” and Foundry. Essentially RW is a template driven software for creating websites. As you know there are lots and lots of templates for sale.
Foundry, in essence, is a non-template template. It’s like starting with a blank page (with Stacks as your tools) instead of color-by-numbers. It (and Foundation) provide much more freedom in terms of how you create webpages.
Some prefer templates, but more and more folks (intermediate to advanced) are using the non-template open-ended approaches offered by Foundry and Foundation.
If you are perfectly happy with the template(s) you are using then Foundry is not needed by you. If you have ever wondered, or been frustrated, that your template does not allow you to easily accomplish some design goal … well, then, Foundry is likely your answer.