[skrowl]

Retina in this sense is an Apple marketing buzzword for high DPI anything. Back in the day they used to have higher DPI items, but today they still put 1080p displays on their 5.5" phones while most other flagships use 1440p in the same size display (and are thus much higher DPI).

[eknkc]

You are right but I wonder if it is any improvement at this point. Writing this on a iPhone 6s Plus and I can't possibly see individual pixels. What is the benefit of going higher?

[sp332]

This is a niche answer, but you can put them in a VR headset with lenses that spread out the screen over a much larger fraction of your visual field without looking too pixel-y.

[skrowl]

Hold your 6S Plus up next to a Note 7 viewing the same photograph or high resolution video. If you don't see a large difference, head immediately to the optometrist.