Well, strange as it may sound, my setup initially required both: running the sanguinololu without and with 5V USB (at different times) - hence, the adapter and not the cut trace.
Without 5V USB: sanguinololu connected to its own power supply running in the reprap connected to a headless raspberry pi - in my basement with no monitor or PC around.
With 5V USb: the bare sanguinololu taken out of the reprap and brought upstairs to my normal PC for firmware flashing using the Arduino IDE and powered by usb.
PS. Since that setup involved removing the sanguinololu and running up and down the stairs too often I eventually discarded the raspberry pi and went for a used PC..
Without 5V USB: sanguinololu connected to its own power supply running in the reprap connected to a headless raspberry pi - in my basement with no monitor or PC around.
With 5V USb: the bare sanguinololu taken out of the reprap and brought upstairs to my normal PC for firmware flashing using the Arduino IDE and powered by usb.
PS. Since that setup involved removing the sanguinololu and running up and down the stairs too often I eventually discarded the raspberry pi and went for a used PC..