To sleep, or turn-off, or leave on, that is the question

Question

A couple years ago I called a local Mac dealer and asked the worth of my G4 iMac for a trade-in. He asked whether I usually turned the G4 off, or put it to sleep, or left it on all the time. I said, I usually left it on (with display turned off), or put it to sleep at night. He said the value was less in that case because the heat stresses in high-powered ICs were more detrimental to the life of the machine than on-off stresses. He said I should always turn the machine off at night.
I'm a retired computer engineer, and the philosophy we had at the time I was working was that the thermal stresses on ICs and solder joints induced by repeated on-off cycles was more harmful than the steady-state stresses of leaving a computer on 24/7.
So, that's my question. What is best for my new iMac for maximum reliability. (Forget about energy consumption for the moment.}
1. What's best for overall reliability - turn the unit off at night, put it to sleep at night, or leave it on (with the display in sleep) - or some variation of these.
2. Is there some magic in the OS that is optimized by one mode over another?
I'm expect there are no comprehensive studies on this subject, but perhaps there are some informed opinions.
-Bob

Answer 1

For a desktop Mac, I leave it ON all the time using only Display Sleep. I also have the setting for +sleeping hard drives when possible+ enabled, but that does not apply to the internal drive (when used as the startup disk); it keeps spinning. External drives do spin down when not accessed.
I believe leaving it on all the time causes less long-term stress on the hardware, for a Mac that is used every day for at least half the day.
I think the second best approach, and better approach for energy conservation, is to use Computer Sleep. However, it should be used so that when you start using the Mac at the start of the day, your Mac stays ON (with Display Sleep only) for the rest of the day. At the end of the day (when you will not be using it again until the next day), use Computer Sleep.
Periodically, for leaving it on all the time or using sleep, restart the Mac; you can make it weekly if you want a routine, but my iMac is fine for about three weeks. After that, I often notice some oddities with general performance, so I do a restart. I don't think about too much, because there is usually some other reason to do a restart within a three week period.
I think the worst approach, which a lot of people use, is have Energy Saver set to do Computer Sleep after a relatively short inactive period. Then, the Mac is repeatedly powering on and off (sleeping/waking) throughout the day, and that probably puts more stress on the hardware.
For a laptop Mac, they are designed to run off battery power and use sleep to save power (and their hard drives are better suited for that mode). The issues and considerations are not the same.