Many of your PICO projects will be self powered and you need a special USB cable to communicated with it otherwise you can damage the PICO or the batteries. Connecting USB while the PICO is powered can also create a safety hazard!.
This video explain why this is a problem and how to take an ordinary and inexpensive cable and make is safe for use. BE SURE TO HAVE THE USB CABLE UNPLUGGED WHEN MAKING THIS MODIFICATION!
Cheers!
Chris