A hub that doesn't have a power supply, is called a bus-powered hub.
If you hook up a bus-powered hub to your MBP, then all gadgets connected to the hub will draw power from the MBP.
Now say you connect three USB sticks to the hub, and each uses about 150 mA while in use, and the hub also uses 50 mA, then at 5V, they use 5*(150+150+150+50) = 2500 mW = 2,5W
But that power is not drawn constantly, because when the USB sticks aren't in use, they would probably drop to less than 30 mA instead of the 150 mA when reading/writing.