So, what use case would you see with ShadowDOM?

I see this more as a way to progressively enhance an element. But in my own use of web components I haven't seen a need for ShadowDOM, but I'm usually just progressively enhancing my page and adding behaviors to my elements. I can see a use case for ShadowDOM when completely creating a new element, but at that point it makes sense to just use a regular web component. Maybe I'm wrong. But that is the reasoning I'm using.