I usually turn my computer on around 9 am for a couple of hours then back on after lunch for a hour or so then sometimes in the evening for another hour. My friend tells me that it's better to just turn the computer on in the morning and leave it on all day turning it off at the end of the day. Which is the best or does it even make a difference?

I have to keep mine on all the time. If I turn it off, it won't start again....the fan gets louder and the monitor won't turn on. I took it to 4 technicians and they couldn't find the problem. So, its always on untill we get a power outage like today....and I have to crawl back to the laptop

There is no doubt that power cycling electronics shortens its life by a measurable amount, most failures occur at power up.

That said, a few cycles a day like the OP is no issue (and saves energy). Personally, my desktop gets powered up in the morning and off when I go to bed as I tend to be on and off it all day.

I usually turn my computer on around 9 am for a couple of hours then back on after lunch for a hour or so then sometimes in the evening for another hour. My friend tells me that it's better to just turn the computer on in the morning and leave it on all day turning it off at the end of the day. Which is the best or does it even make a difference?

I never forget - I had high voltage in my apartment in Pattaya one day. The TV burned down - the computer lost only the PSU - I unplugged the monitor immediately. But since that time I always switch off everything when I leave my room. I learned that many homes do not have grounding and the fuse will be the last thing that will be left if a home burns down ;-)

There is no doubt that power cycling electronics shortens its life by a measurable amount, most failures occur at power up.

That said, a few cycles a day like the OP is no issue (and saves energy). Personally, my desktop gets powered up in the morning and off when I go to bed as I tend to be on and off it all day.

I do exactly the same thing.

Maybe a bit off-topic but thought quite interesting.

How Much Electricity Does My Computer Use

Typical PC at a business:

Computer running 8 hours per day with 17″ CRT on for 8 hours per day = $56.94 per year.

Computer running 8 hours per day with 17″ LCD on for 8 hours per day = $39.86 per year.

*Computer running 24 hours per day with 17″ CRT on for 8 hours per day = $110.08 per year.

*Computer running 24 hours per day with 17″ LCD on for 8 hours per day = $93 per year.

*The computers above that run for 24 hours are set to not sleep when they are not in use.

Typical PC at home:

Computer running 4 hours per day with 17″ CRT on for 4 hours = $ 28.47 per year.

Computer running 4 hours per day with 17″ LCD on for 4 hours = $ 19.93 per year.

*Computer running 24 hours per day with 17″ CRT on for 4 hours per day = $ 94.90 per year.

*Computer running 24 hours per day with 17″ LCD on for 4 hours per day = $ 86.36 per year.

Source: Maximum PC Guide

my iMac is on 24hrs per day, the last time i restarted it was 2 weeks ago when i moved it from the bedroom to downstairs. The screen switches off after 5 minutes of idle and that's it. Maybe i will reboot once per month if i feel inclined.