The Pros and Cons
Manual tuning uses fixed numbers that you type into the code yourself, making the LED behave exactly the same way every time you turn it on. It is reliable and won't get confused by sudden flashes of light, but you have to guess the numbers and rewrite the code if you move the circuit to a different room. Auto-tuning lets the Arduino find the room's light levels on its own, so you never have to guess numbers or change the code. It adapts to any room instantly, but it can act glitchy right when you plug it in and will get confused if a sudden bright light flashes on the sensor.