I often use Hibernate during the day or even overnight without any problems - in fact my best mate's laptop (an elderly 500Mhz Pentium) is always shut down in Hibernate mode, although I've persuaded him to do a regular proper shutdown to keep things sweet.
The benefit, of course, over Standby is that all settings etc are retained and resume on bootup.
Standby leaves the machine 'powered up' but inactive. ie main power going in,drive running .
Hibernate, allows the user to stop in the middle of an activity - writinga letter say - the machine will record what is happening onto HDD - power down - whereby you can switch of at the wall socket, unplug even, and when you start agian next day, next week even - the page will come to desktop just where you left it. I do it all the time, my pupils when I showed them think is great..
Thanks for all the info. What I am really cocerned about is whether leaving in standby ,sayovernight, does any harm. Standby is useful because it seems to switch everything off ie. fan and hard drive yet I can quickly resume by moving mouse.
Leaving the machine switched on is not likely to give rise to any concern.
The real concern is that you don't appear to be taking any notice of the advice you are being given re the difference between Hibernate and Standby.
I'll repeat. Putting the system into Hibernate state preserves all the settings etc at that point and you return to the status quo on startup; using Standby is different and, if for instant, you suffered a power failure, then you can guess the rest.
Thankks to all responders,particularly Stuartli, I did appreciate the diff between Hibernate and standby but I suppose what I was really concerned with was whether leaving the computer on permanently accelerates wear on components,particularly the fan. Thanks anyway.
It's a moot point as to whether leaving a machine turned or turing off (e.g. daily) on decreases it's lifespan the most.
Some would argue that turning off some components and turining them on again (esp. the HDD) causes more harm them leaving turned on.
For my part, I close down and reboot every day (and all my boxes are several years old and suffer no hardware probs). Firstly it is ecologically sound. Secondly it is good practice as any changes that might give rise to re-boot problems become known v. soon after the changes are made. Imagine not rebooting for many months and then finding major problems - how would you focus in on the likely cause?
Lastly, although XP is better than previous versions of Windows, a freshly booted machine tends to run better than one that hasn't been rebooted for a while, as the runtime environment is reset.