Pixel OFF uses Amoled's unique feature that it can turn off individual pixels completely. It turn off some individual pixels, reducing the power draw by the display
Ranked in these QuestionsQuestion Ranking
Pro Adjustable agressiveness
There are 5 levels to choose from - Mesh 1 is the lowest setting, and Mesh 5 is the most aggressive. You can choose which level to run at to best compromise between battery life and picture quality.
Pro Reduces power needed by the display
Pixel OFF basically overlays a black grid over the existing picture to prevent some pixels from lighting up at all. This reduces the overall power draw from the display
Con Reduces picture quality
Because it overlays a very thin black grid, it is effectively reducing the resolution of the display...however the pixels won't be spaced out properly (for example instead of having 8 pixels evenly spread out, now you could have 4 regular pixels followed by a black pixel, followed by 4 more pixels and another black pixel. This will distort the image.