You're likely to get many opinions on this.  With a desktop I was told that the main problem was the temperature cycle that the hard drive went through when the power was turned on and then off.  Many businesses have the users leave the computer on 24 hours a day, partly on the theory that the relatively constant temperature preserved the hard drive, and on the fact that it made it easier for the information management folks to perform updates.  My own desktop at home runs for days at a time, but if I don't expect to be operating it for a while I turn it off.  You need to remember that it also consumes 200 to 300 watts while running and that this can have an impact on the electric bill.

With laptops I was told that the machines weren't designed to support 24/7 operation.  I don't know if this is true, but since my laptop spends a lot more time not being used than being in use, I turn it off when I'm done.  You should also consider the battery life with a laptop.  Most rechargeables do not get their maximum life expectancy if they are left on charge continuously without a discharge cycle.  You don't want to take a lithium ion battery all the way to zero as this also shortens its life, but every two to four weeks it should be used to power the laptop until it reaches about 20% capacity or thereabouts.  I also unplug the laptop when I'm not using it.  I can't say that my procedure maximizes battery life, but I know mine has lasted over a year so far.

Bottom line is it is your preference.  I hope you enjoy your machine for a long time to come.

 

What he said.

Thank you!

The system can stay on all the time But Monitors have a limited life. CRT tends to last longer than LCD but either burns out the light after so many hours. If you leave the PC on turn the monitor off.