Progressive Web Apps are also known as PWAs.
They come with a few benefits that developers can take advantage of to improve the experience of their site visitors.
Some of the benefits include:
Offline Mode. This allows visitors to revisit sites they've previously visited. This works because PWAs store a version of the site as an offline app in that user's browser. Similar to a cache but more than just the pages the user visited. It often includes the entire site.
App-Like Experience. PWAs feel snappy and provide an experience that feels more like a native app rather than browsing a website page by page.
Performance Benefits. Along with the app-like experience and offline mode users who are repeat viewers of your site should be able to access your site and browse faster. With the exception of that initial first view which could be longer since it has to load all of the necessary files for that PWA experience.
Push notifications. You can do a lot with PWA and push notification is just one of them. Note that features like this are available but you do need to configure them. Whether you're doing this with other WordPress Plugins or creating custom functions, all of this is possible but you need to configure it.
HTTP/2. Progressive Web Apps are going to help Shifter users take more advantage of the HTTP/2 advantages we offer. This is a feature that resolves "render block" and allows site visitors to download assets from your site all at once. Have a large CSS file? Don't sweat inlining it, with HTTP/2 and PWA that won't block the browser from downloading the rest of the site.
Shifter + PWA + WordPress FAQs
Is PWA added or enabled automatically?
Why this particular WordPress Plugin and not others?
We have decided to support this PWA WordPress Plugin as a first step. This Plugin is also the most likely candidate for a merge with WordPress Core. If or when that happens we'll be ready!