An USB isolator allows get rid of ground loops and reduces electromagnetic interference (EMI) amongst the pc as well as the related unit. 1x GND 3V3 (P2 with 2 pins two.54mm) connector can be used to power externally the WCH CH569 MCU (it is suggested to eliminate the P4/SHUNT in https://mariocumdt.wikinarration.com/6630323/indicators_on_hydrabus_you_should_know