A diode will drop about 0.5-0.6 volts, which could eat 10% of your energy, so reverse polarity protection is usually used in devices where someone could plausibly install the batteries backwards. I think it's probably rare on something on a highly controlled standard connector like USB.

It's fairly easy to do it without the diode drop if you use a mosfet, but you do incur the cost of a more expensive part.

It's usually common in low voltage, low current devices. I have a massive inverter charger on our boat that has in giant letters "NO REVERSE POLARITY PROTECTION". It typically handles up to 200amps at 12V.