The PowerBlock provides a Raspberry Pi power switch functionality. Why is it useful? The Raspberry Pi comes without a power switch. As soon as you plug the USB cable into the Raspberry, it turns on. If you want to shutdown the Raspberry Pi, you need to call a shutdown command to bring the system into a state in which you can safely remove the power cable again. If you just pull out the power cable the file system of the Raspberry might become corrupted and you risk losing data.
Here, the PowerBlock comes into play for safe shutdowns. It is stacked onto the GPIO header of the Raspberry Pi and provides a USB connector itself, a connector for a power button to control the power supply of the Raspberry Pi, and a connector for an optional LED to indicate whether the Raspberry Pi is off, booting, running, or shutting down. A micro controller on the PowerBlock board manages the power supply and monitors the button state as well as the state of the Raspberry Pi. The driver ensures that a clean shutdown is done when you switch off. This also means that you do not need to plug and unplug the USB cable from the Raspberry anymore if you want to completely and safely turn it off.