Imagine if there was no lag opening any app because everything was in memory. Imagine your code getting simpler because you don't need to load assets off disk - that's done all in one go at boot time. You want to render an image out? Just do it - a reference to a file is a reference to a file, no loading it or wondering if it's loaded.

Flash storage in phones is fast enough these days that it's probably not worth it, and simply giving traditional phones lots of RAM will probably give 80% of the improvement for 20% of the cost. But I've been curious about the idea for some time.