This USB 3.0 cable is made for connection and additional power supply of your USB 3.0 devices. Thus you can connect e.g. external 2.5 or 3.5 HDD enclosure etc. by using an optional connecting cable, to your notebook or PC without additional power supply.
Note: For operation of a 3.5 HDD without extra power supply, you need to connect the HDD to an active USB 3.0 and USB 2.0 port.