Define intensive.

But any well architected app that wants to work well without Internet will write many things to disk.

500 writes a second is very realistic when downloading some bulk content that will be used to power different states of the app. Now this might not be a continuous burst of 500 operations a second sustained, but many it has a handful of these bursts over several minutes. Given that, I would say that lots of mobile apps can have brief periods of tons of writes.

Just write a chat or email application that persists your conversation on disk. It goes crazy at times.

On Android most well-architected applications will persist almost everything to disk before showing it to the user. Network directly to UI is too unstable.

It's not about intensive reads/writes (dozens of MB) it's about making each individual read or write very fast so you don't drop frames. On Android you have 16ms to draw each frame (60fps). If you have a DB request take 5ms then all of a sudden you're very likely to have jank in your app.

Don't do I/O on the UI thread. The time it takes to do a write should not affect jank.

Yeah, a well architected application doesn't touch disk on the UI thread.