What is a Service Worker's role and key PWA capability?

This question tests whether you see the Service Worker as a network proxy, not merely a background script. A strong answer covers three things in order: first, that it intercepts application network requests; second, that it enables effective offline use via granular caching; and third, that it also enables push notifications and background sync. Red flags include conflating it with general Web Workers, claiming DOM access, or calling it purely a performance optimization without mentioning request interception.