Best use case of this I guess, is some kind of flight mode for web apps. Before going in to metro or flight, you click a button, and for example HN caches front page for you.
Service workers have access to Indexeddb but not to local storage. That's something to remember.
[0]: https://developers.google.com/web/updates/2015/12/background...
> Sync events will often complete while the user has a page open to the site, so requiring user permission would be a poor experience. Instead, we’re limiting when syncs can be registered and triggered to prevent abuse. E.g.:
> You can only register for a sync event when the user has a window open to the site.
> The event execution time is capped, so you can’t use them to ping a server every x seconds, mine bitcoins or whatever.