In general, the shadow DOM will have positive impacts on performance. Right now when you insert an element on a page it inherits all of the CSS of that page and

In general, the shadow DOM will have positive impacts on performance. Right now when you insert an element on a page it inherits all of the CSS of that page and must be evaluated accordingly, whereas a shadow DOM element can have a very small set of styles associated with it. These benefits won't be realized until the shadow DOM is fully implemented, however.