I've been working on mobile apps developed for education in Afghanistan, rural Rwanda, etc for the last 9 years. I used to think that sync was the way, but I have learned from painful experience.

4 (extended): What happens when the user has access to millions of items, but they probably only want a few (e.g. an ebook library catalog)? Do you waste huge amounts of bandwidth and storage to transfer data, of which 99.9% will be useless? We had a situation where the admin user logging in on a project that had been running for years resulted in a sync of 500MB+, 99.99% of that data the admin would never directly use.

Also: do you make users wait for all that old data to sync before they can do anything when they login?

Relying on sync is basically relying on push-only data access. I think in reality most offline/local first applications will work best when they push what a user probably wants (e.g. because they selected it for offline sync, starred it, etc) and can pull any other data on demand (in a way that it can be accessed later offline).

I've outlined that here: https://medium.com/@mike_21858/auto-generating-an-http-serve...