seemingly the story with the “two usb’s for power” thing is that…
anything before usb 2.0 doesnt supply enough amperage to bus power devices like laptop harddrives and these slimline bus powered drives, thus you have to double up the supply connection to achieve a working device.
you will only ever have to use two usb ports or an external power supply if you are using a system that is too old for the usb 2.0 standard (assuming that the device is meant to be bus powered).
so don’t panic if you lose your double plug usb lead! 🙂