You'll get lots of differing opinions on this as it's largely personal preference and not really an energy consumption or wear and tear issue any way you go.

I leave mine up most of the time, with the monitor set to go off after 15mins.

I'd suggest that you try different modes/times until you find the one that works for you.

Well, here's the thing.  Turning your PC on and off increases the wear and tear, which can reduce the life of your components.  Of course, those components will most likely be obsolete, and replaced, long before they fail, so who cares?  By turning the PC on and off, you also save energy, but only something in the range of 15 bucks a year, so who cares?  In other words, it doesn't really make much difference either way.

One caveat: avoid hibernation mode.  It was designed for laptops rather than desktops, and while more often than not it works fine, I've sen it cause some very thorny problems.

Personally?  I leave mine on, with the monitor in standby after 15.

thanks for all the info...I will aovid the hibernation mode....what about the turn hard disk off feature? 

I don't use it because I need my tower running, since it provides an ad-hoc network connection.  It certainly won't hurt to use it otherwise, though.

By turning the PC on and off, you also save energy, but only something in the range of 15 bucks a year, so who cares

Last year I checked my Dell 8200 system and 21 inch monitor with a watt hour meter... leaving it on 24/7  would cost $220. a year.

Running it for 12 hours a day would cost $110. a year.

I only used $0.10 cents per KWH to figure the cost... most folks pay much more than that.

Besides the more the computer fans run the more dust is pulled into the computer. It does not shorten the life of a computer shutting it down. I have a IBM that has been shut down several times a day for six years and no hardware has failed.

 

I think you misunderstood.  Obviously the difference between the power usage of a PC at peak performance and the usage when it was turned off is huge.  I compared the usage when off to the usage in standby mode.  The margin is a lot smaller.  Online, I looked up the average power consumption of a PC in standby mode.  At my area's rate of around 20 cents KWH, the savings are negligible.  That's why I recommended powering down the monitor and hard disks.

I also should have listed this;

Actual readings using a watt hour meter:

Monitor in standby (off), hard disk off,  usage was .1041 KWH compared to .2507 KWH with all systems in operation. This included a cable modem and a router that is on 24/7.

With power management I have my monitor and hard disk set to shutdown within 30 minutes of no mouse activity. I never use the hibernate mode.

If I'm not going to be using my computer within the next couple hours I shut it down and flip the main switch at my desk power panel.

This procedure has worked great on my other computer and besides saving power it gives added lighting protection.