Energy reduction cannot be ignored
It is interesting to see the debate on leaving PC's on 24/7 still going on. As has been previously pointed out, the hardware in modern PC's has changed significantly and there is no reason now to keep a PC on permanently.
The amount of extra draw on the power at boot up is marginal compared to a PC being left on, even when in sleep mode. The efficiencies of PC's heating a room compared to a specifically designed heater device is ridiculous.
In the corporate environment patching, updates and backups are mainly performed out of hours, which is why Wake-on-Lan use allows PC's to be woken up when these tasks need to be performed. Remember patching and critical updates are not a nightly event, and A/V updates can be scheduled during working hours, especially if they come from local sources.
There are applications (we supply 1 - I wont advertise here though) that fully manage this capability, including setting daytime power saving states, automatically shutting PC's down, booting them up, whether for updates or to be ready to go first thing in morning and have demonstrated significant cost savings. The cost of a PC running 24/7 can be anywhere from £34+ per year. Creating an efficient power management policy can bring this down to £10.
Whether a companies focus is on energy saving, reducing their carbon footprint or the cynical PR angle energy waste of such size cannot be ignored.