This is so simple. You plug your PC into the main socket, and then plug your printer, scanner, monitor etc into the other sockets. When you turn off your computer, the smart unit shuts the power off to the other sockets. Saves power from constantly-on transformers, saves the environment, and saves lives from electrical fires caused by overheated DC adaptors. Also works for AV equipment.
A cool tool is anything useful that is superior to comparable items. If you think this tool is inferior suggest a better one. You are welcome to insult a tool, but comments containing insults to individual people will be deleted. Corrections of fact are always welcomed, if stated politely. Recommendations of better tools are dearly wanted and may be elevated to the front page.