I don't know where you got that, Fox, but I've heard the same urban legend approximately ten bajillion times.
In actual fact, entering 'sleep mode' (note: not hibernate, that's different) takes more power than shutting down and rebooting does. Why? Because the system keeps drawing power to keep the contents of RAM alive. During shutdown, obviously, it doesn't. And starting up doesn't cost anything extra -- your hard drive is essentially drawing the same power whether it's been running for half an hour or if it's just starting up. The tradeoff between shutdown and sleep isn't power, it's speed -- sleep is almost instantaneous, shutdown-and-reboot is not.
Hibernation mode is slightly different, in that it's faster to start up from than shutdown but slower than sleep, and it has some of the advantages of both -- it uses no power at all, but the state of your computer is preserved. However, it has some issues -- not everything out there is truly compatible, and it often chokes on connected devices (which themselves aren't designed properly); when it works, it's great, but when it doesn't work you might as well have saved yourself the frustration and just shut down the first time.
TL;DR version: always shut down your computer if you're going to be away from it for more than thirty minutes or so; if less, sleep it. That'll give you the best balance of power saving vs. convenience.
--sofaspud
--"Listening to your kid is the audio equivalent of a Salvador Dali painting, Spud." --OpMegs
In actual fact, entering 'sleep mode' (note: not hibernate, that's different) takes more power than shutting down and rebooting does. Why? Because the system keeps drawing power to keep the contents of RAM alive. During shutdown, obviously, it doesn't. And starting up doesn't cost anything extra -- your hard drive is essentially drawing the same power whether it's been running for half an hour or if it's just starting up. The tradeoff between shutdown and sleep isn't power, it's speed -- sleep is almost instantaneous, shutdown-and-reboot is not.
Hibernation mode is slightly different, in that it's faster to start up from than shutdown but slower than sleep, and it has some of the advantages of both -- it uses no power at all, but the state of your computer is preserved. However, it has some issues -- not everything out there is truly compatible, and it often chokes on connected devices (which themselves aren't designed properly); when it works, it's great, but when it doesn't work you might as well have saved yourself the frustration and just shut down the first time.
TL;DR version: always shut down your computer if you're going to be away from it for more than thirty minutes or so; if less, sleep it. That'll give you the best balance of power saving vs. convenience.
--sofaspud
--"Listening to your kid is the audio equivalent of a Salvador Dali painting, Spud." --OpMegs