One main benefit I can see from Web Components is that it allows you to front-load the implementation code for common components to the browser, which can hypothetically be far better for performance than including custom, non-standard javascript libraries on every website you visit. Since browsers are either bundled with mobile OSs (or they are a big, one-time download), users don't have to deal with the performance cost of rendering Your Custom Component Script for every website they visit. Conceivably we can move towards a mobile web that is highly interactive with very little payload cost in terms of loaded javascript and CSS.
That said, the obvious downside is how customizable and cross-browser these components will eventually be. As your components get more complicated, adding more html attributes to customize your element becomes prohibitively harder. I'm interested to see how they tackle this problem.
That said, the obvious downside is how customizable and cross-browser these components will eventually be. As your components get more complicated, adding more html attributes to customize your element becomes prohibitively harder. I'm interested to see how they tackle this problem.