Why two cables for my Buffalo Ministation

[palladrj]

Hi All,
My Buffalo Ministation TurboUSB Portable Hard Drive has one miniUSB input and one power input. The drive came with two cables. One is the standard USB with a mini on the opposite end. The other has a male power connector on one end and a USB connector on the other. The device is powered, and will run with only the mini on the HDD and the standard USB connected to the laptop. Does anybody know the purpose of the other cable?

[not important]

My experience: I have a 2.5" external that came with a mini-USB plug on one end and a dual standard size USB plugs on the other end of a single cable. One of my PC's requires BOTH USB plugs to be connected to operate the drive. My other PC's and a laptop will operate the drive with only one USB plug connected.
So, I'm assuming the extra plug is for PC's that would require the power plug.
I hope this makes sense.