for the lifetime of your computer, it wont make much difference, long term its better for the hardrives inside the pc to be left on 24/7 (spin down/spin up causes harddrive streee some will say) but for home pc use it dont really matter

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Beware of killer hamsters and the random running dogs.

agreed, it wont really make much difference, the longer you leave your computer on the more you'll notice a deterioration in performance - programs that you've opened will not allocate all of the RAM it required in order to be ran back to windows so you'll notice a gradual decrease in speed. I turn my computer on and off all the time - unless it's a server i'd personally suggest restarting it / shutting it down every 3 or 4 days dependant on the above mentioned decrease in performance. With home pc's if you leave your computer on for weeks the CPU fan will eventually get used to spinning round, when you go to turn it off and back on again after a period of a few days you might find that the fan will have siezed. Leave it on as long as your wallet can afford the electric bill mate.

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