John Backo answers the question: “What are those lights on the nano anyway? And do I need them?”
There are usually 4 LEDs on the nano. They are usually in a row and labeled “RX TX PWR L”.
The RX and TX lights are connected to the lines that connect both the USB interface and the ATMega628P. They connect to TX0 and RX0. They are very useful as their flashing shows that communication is taking place during an upload. Likewise, if RX flashes once and then not again during an upload, there is a communications problem. Usually they are red and green; some may be orange. Messing with them will probably mess up RX0 and TX0. It is best to leave them alone. They are always out (low) with no serial communication to the chip. If they stay on, something is wrong…
PWR refers to a direct connection to the voltage regulated 5v line. It is NOT connected to the input voltage, whatever that may be. It is an indication that the board has power either from Vin or USB. That is all it does. It is usually red though I have seen many orange lights. It is useful, but it could be eliminated, I guess.
L is connected to D13. It is a good light and should not be disconnected. If the ATMega has a bootloader (which it should in a nano) this will flash three times when the reset button is pushed and released. That is not guaranteed because earlier versions of the bootloader did not show themselves through D13. And if the ubiquitous Blink program is loaded, it will falsh D13. That alone makes it a good light to retain. It is your “diagnostic visual indicator”.