This matters a lot with machines like thinkpad x60:
thinkpad x60 [75Wh] ~~~~~~~~~~~~ init=/bin/bash (HZ=250) 14 W disable USB and sound: -3.6 W
..the list goes on with:
idle machine: +0.2 W intel console +0.4 W idle machine, min bl, intel console: 14.6 W HZ=250, no usb/sound: 11.0 W HZ=100, no usb/sound: -0.3 W (?) HZ=1000, no usb/sound: +0.2 W (?) bluetooth enabled + ipw on: +1.4 W bluetooth enabled: +0.1 W max bl: +2.1 W (?) + 3 W (when max enabled in bios?) no bl: -0.9 W ethernet cable inserted + ifconfig up: +0.4 W kernel build (one cpu): +19 W kernel build (two cpus): +28 W lower refresh rate (60Hz -> 43Hz) -0.05W vga=1 ... -0.5 W or so SVGATextMode 40x12x8 -0.2 W (additional) white background instead of black -0.05W Xwindows +0.1 W (+0.3W?) Xwindows, 8bit depth -0.15W Xwindows, 8bit depth, 640x480 -0.35W hdd spindown -0.5 W (?) sound off (echo -n 2 > power/state) -0.3 W cardbus bridge off -0.03W (?) firewire off -0.00W (?) mmc off -0.00W (?) e1000 off -0.00W (and driver confused?) ide controller off -0.01W smbus controller off: -0.00W SATA controller off: -1W (and machine dies) docking station +1W fan: +0.3W (!)
...as you can see, USB and backlight are the entries that matter most. It also explains why I'm playing with SATA/SCSI power management now. Getting the SATA controller off is quite important.