Whether or not you need to isolate a USB device from your computer is dependant on the application. When connecting a flash drive, isolation is rarely necessary. However, if you are connecting industrial instrumentation or remote I/O equipment to your computer, there is no easy answer. You must evaluate the environment in which the device is installed. Is the device is susceptible to ESD (electrostatic discharge), lightening, power surges, ground loops, differing ground potentials, EMI (electromagnetic interference), or RFI (radio frequency interference).