Joshua Ho, AnandTech:
Realistically, humans seem to only be able to have a practical resolution of around .8 to 1 arcminute. So while getting to 600 PPI would mean near zero noticeable pixelation for the vast majority of edge cases, the returns are diminishing after passing the 1 arcminute point. For smartphones around the display size of 4.7 to 5 inches in diagonal length, this effectively frames the argument around the choice of a few reasonable display resolutions with PPI ranging from 300 to 600. For both OLED and LCD displays, pushing higher pixel densities incurs a cost in the form of greater power consumption for a given luminance value.
This is as in-depth as you’ve come to expect from AnandTech.