Richard Feldman gave a talk at Elm Europe about the principles he used to build his Elm Single Page Application elm-spa, and we highly recommend watching it! It's called Scaling Elm Apps. post 
YOUTUBE DoA4Txr4GUs Elm Europe 2017 - Richard Feldman - Scaling Elm Apps
The use cases:
1. The user has a fast connection 1. The user has a slow connection 1. The user is offline
# Offline
Feldman wants at least some things to work while the user is offline.
YOUTUBE WqV5kqaFRDU "Web Apps without Web Servers" by Richard Feldman
He didn't go so far as to use Service Worker (or App Cache, for those of us who went that bumpy road), but he wanted users to be able to visit pages like New Post that could be loaded without retrieving data from the network. For these pages, init returned a model instead of a Task PageLoadError model. That was all it needed.