Progression is just an idea, not a practice.
“The premise is refreshingly simple: bridge the gap between offline and online experiences and gain performance increases, lower bounce rates, and even better conversion rates while doing so. Progressive web applications (PWAs) are basically another layer to add on an existing website, one that interacts between the browser and http connection. This means that any and all requests first go through the service worker, which is an important part of any PWA. The service worker then determines whether there is even a need to connect to the internet for the request, or whether it should just serve a locally stored cache of the website the user is currently browsing.”