If you follow smartphone product launch news for the upcoming year, you will see all the flagship models now have 1080p 5 inch screens with a 441 dpi super retina display.
Meh. You can't see the difference between 1080p and 720p on such a small screen. Hell, I couldn't even see it on my old 32" and 42" LCDs. You need to go up to 50" and above to see the difference between 720p and 1080p.
You can't see the pixels above a density of about 300ppi. So, what is it good for? Absolutely nothing.