Una explains in Implementing "Save For Offline" with Service Workers
I recently added an option to save blog posts for offline reading, and this post will detail how I did that so you can too.
I really like this idea. One of the reasons I never rushed into adding a ServiceWorker to this site is also mentioned by her:
By giving our users the option to save a post for offline reading, we're not taking up valuable space in their cache without permission.
Looks like I'm not alone with this thought.