It appears that the "Scaled" as "More Space" setting merely renders everything in HiDPI mode (2x widget size) with a canvas render resolution of 3840x2400 and then scales it down on the 2880x1800 display.
Just download the image linked above and display at as "Full Screen" and "Zoom to Fit" under Preview on an existing 15" MBP—it'll give ya an idea of what the "More Space" setting scales visual elements as.
It appears that the "Scaled" as "More Space" setting merely renders everything in HiDPI mode (2x widget size) with a canvas render resolution of 3840x2400 and then scales it down on the 2880x1800 display.
Just download the image linked above and display at as "Full Screen" and "Zoom to Fit" under Preview on an existing 15" MBP—it'll give ya an idea of what the "More Space" setting scales visual elements as.