As an individual you may not care much, but at a wider scale can be a noticable impact on power usage.
If every household in the US (~120m) draws an extra 10w average power, total requirement is arround 1Gw or 1 extra mid/large size coal/nuclear plant (E.g. Three mile island).
If you start adding all the devices you have on standby (inclucing some of the nasy cable boxes that drew upto 50w standby) it starts adding up. This is esentially where the EU regulations for standby power came from in conjunction that for most devices is it costs almost nothing per device to have it use minimal standby power just a bit or care and effort in the design phase of a hardware project.
* Ignore for simplicity that if running heating power is not really wastes, but if running household aircon essentially you double the power usage.