When you have a power supply that's not SATA 3.3 compliant and a drive that supports it. The SATA 3.3 revision revised one of the 3.3v pins to be a power disabl

When you have a power supply that's not SATA 3.3 compliant and a drive that supports it. The SATA 3.3 revision revised one of the 3.3v pins to be a power disable pin. Almost no hard drives support it so it's not really something you'll run into but consumer external drives will often be ordinarily super expensive enterprise drives in a plastic shell. Google the SKU of whatever external drive you're thinking of shucking to find out if it needs a SATA 3.3 power connector and instructions on opening it without damaging it in case you ever need to warranty the drive.