"Set the overall preset of graphics quality." Sets every other option to the selected value at once. When set to low, the overall color and atmospherics of the scene are hardly changed, along with the model quality and bloom, but textures become very blurry, lighting and shadowing are inaccurate, and the grass is less dense. IMPORTANT: this is tied directly to the quality of light shafts. Turning this to medium or lower and every other option up to very high will result in about a 10 FPS increase at the cost of lower resolution light shafts.