We all started using Gmail because synchronising to a mail server is annoying and PCs where slow. Ten years later machines have a fast internet connection, 1TB HDD as standard and, maybe an SSD. When you have to wait 10 seconds just to view an attachment syncing makes a lot of sense. But generating a thumbnail of that same PDF would be much better handled pre-emptively in the cloud.

The problem is believing that one approach is better for every function of an app. Few user machines will ever have a guaranteed large amount of bandwidth. This is just as true on desktop machines as mobile, but less acknowledged.