USB hubs are used to enhance the capacity of the computer to hold more than one device. The device can be in different design but the most known are the octopus style which uses different small cables to connect between themselves; and the star style in which the ports are together.
The USB hubs are normally used by people who have more than one device to connect to the computer. The USB hubs are used to connect the printer, the camera, the flash disc to the computer without the hassle of always having to unplug and to plug the devices if there is a need to use a different device. If the computer like the laptop has to be moved around so much one can use a USB hub so that you can plug-in or plug out all the devices at once. Some of the USB hubs have their own transformers which supply the power to the bus without putting much pressure on the computer power supply.
The different USB hubs are used according to their capacity of being self powered or having to use different source of power. The unpowered devices like the mice or flash disks need the self powered USB hub because they can not produce the power themselves. But if the device has a different source of power than that of the computer, you can use the USB hubs which are not self powered because they can use the power from the devices.
The USB hub can be connected together to make a chain of USB hubs which can connect more than one devices.
The USB hub speed depends on the hub themselves but when more than one hub is connected, the hubs may interfere with each other. The USB hub which has the highest speed by now is the USB 3.0. When the hub is connected to a host; the data from the host are distributed among different connected hubs and the one it is designated for will be able to translate the data. But if the data comes from one of the connected hubs, the data goes directly to the host hub without passing through other connected hubs.
So if you are tired of unplugging and plugging in each time you have to change a drive, why not get yourself a USB hub? It will not only save the time but it will also enhance the safety of your computer.