typical lcd panels require a backlight for them to function as the lcd does not produce light. depending on which colors are turned on rgb you get rgb or b/w. however, even with the pixels turned off (to get black) you often get dark grey at best since the backlight still needs to be on for adjacent pixels. this can result in things like "clouding" or bright/dark spots depending on what kind of backlight you have. grid array shows much less of this.
oled uses small leds which emit light on their own so do not need a backlight.
what are the major benefits of this? highly increased contrast and deeper blacks. basically the same principle of plasma which uses cells which...