With the service enabled, the mesh of black pixels will overlay any app that you use, so even your brightly - colored apps are now a bit more AMOLED - friendly. (android.gadgethacks.com)
In other words, the more black pixels being used, the less power it takes to display it. (androidcentral.com)
However, OLED displays can light individual pixels, and black pixels do not light at all. (cultofmac.com)