Turn PC off every night or leave it on 24/7?
My friend and I have been debating on whether or not there are benefits to leaving your computer on as opposed to turning it off when you are finished using it for the day.
My stance is that I have always turned my computer, speakers, and monitor off after every session. If I am still in my house and just downstairs watching a movie, I will usually leave it running, but if I am going out, going to sleep, or just not using it for an elongated period of time, I shut it down.
His comparison argument was burning out the filaments inside a light bulb from turning the lights off and on to damaging your computer by turning it off and on. He stated that since he goes to a tech school that his comparison remained valid whereas I attempted to reason with him that light bulbs are not electrically wired like a computer's power supply.
Turn off PC or leave it running?
Your friend is right in theory, temperature cycles are not good for any kind of material, however temperatures don't get anywhere near high enough inside a computer for this to be a serious problem. His light bulb example is pointless, he's comparing something that heats up to 3000C vs. <100C. The only argument he can make is that moving components such as HDD are better off running 24/7, because there is less chance of a mechanical failure when something is in perpetually in motion rather than if it comes to a halt frequently. But that's not enough to justify leaving your computer on though. The amount of money in power savings over the years can buy you more than a replacement HDD. And this argument is also moot if you have SSDs.
Plus there's a whole bunch of other good reasons:
• Less energy used
• Many fewer hours on moving parts which includes fans/fan bearings
• Less dust accumulated internally because of fewer running hours; reduces cleaning maintenance
• Less exposure to the chance of a catastrophic event such as a line power failure or even an internal computer failure which might result in a fire (eg, unattended PSU blow out).