You deploy application once on the web and it can be installed on desktop or mobile device as native app, if user chooses to do so. Or used as webapp in browser.
When installed your app has homescreen/desktop icon, opens in separate window.
And the best thing - you don't need to pack a whole internet browser with your app (Electron) and worry about pushing updates to user - you just update your app on web.
Imagine, that instead of downloading desktop client for Slack, you go to slack.com and click "Install" button.
Current negatives are that PWAs still missing support for advanced features like file system access, but browser developers are already working on it.
I hope in few years installing VSCode will be as simple as going to their website and clicking "Install".
