Well I don't leave peripherals (printer, speakers, etc.) turned on at all, only when I need to use them.
One thing that does need to be pointed out here: In 'shutdown' state a desktop computer is still consuming power, and the difference in power consumption between shutdown state and hibernation or sleep mode is so minor as to be completely negligible.
The only way a desktop computer will consume zero power is to switch it off completely, either via a PSU switch or at the power point.
So, when we say "switch off" we are talking about completely switching off and not merely using the "Shut down" option in Windows.
Another point for consideration: We do not
completely turn off other electronic entertainment devices such as TVs, DVD players, home theater equipment, etc. When we click the power button on the remote control, those devices stay in stand-by (or readiness) mode and are still consuming a small amount of power.
Also, in terms of power usage in the average household, the home computer would be very at the very bottom of the power consumption chain.
Not debating one way or the other here, just putting forward some observations for consideration.