An USB isolator will help reduce ground loops and cuts down electromagnetic interference (EMI) among the pc and the linked machine. 1x GND 3V3 (P2 with 2 pins 2.54mm) connector can be employed to energy externally the WCH CH569 MCU (it is suggested to eliminate the P4/SHUNT in that situation It's not necessarily mandatory because the 3V3 LDO IC1