It is very nice of you to have shared so much with us, especially about detailed studies. As regards to fans(old models) at homes, I’ve seen fans functioning for ages that were switched off more than once a day. May be, it depends on design and quality too.Probably, it is a bad idea to switch on & off without complete cool off for the motor/gear. I’m not sure either.As you say, it is difficult to generalize.

I was on various aircraft Reliability Teams but had years of interface with the other teams. The Office Teams learned that the computers in
Reservations, Cargo, Maintenance, and terminal counters that ran 24/7 lasted just as long, and some times longer, than office machines that were turned off every night. But some didn’t.

After detailed studies by three major airlines, it was not conclusive
either way. So, the issue became time and wasted energy.

As noted, I use hibernation every night and have for some time. I like to resume where I left off the night before, and save the energy.

But it’s simply not a proven fact that switching off an electrically driven motor device every day will positively result in longer life.

It might, or it might not. It’s been debated for years.

And I would challenge the notion that switching a device off and on every day is less wear on mechanical devices. Some yes, some no.

This has been debated for years, and I have never found conclusive proof either way. That said, I’m retired from Trans World Airlines and they spent enormous time and effort studying this dilemma. We had thousands of mechanical devices around the world. This began when we left hanger lights on 24/7 and they lasted longer. This was confirmed by American Airlines and Pan American Airlines who followed our maintenance plan. Of course, this was due to heat, getting hotter and then colder caused the lights to fail early.

The concept was then spread to hundreds of mechanical devices throughout the company world wide. Airlines do stick together, at least in those days. We exchanged maintenance records with the other airlines. After doing this for many years with thousands of devices, there was no conclusive proof either way.

It seemed to vary with the device. So, some we left on 24/7, and some we turned off every day.

Hard drives used to be have an MTBF of 100,000 hours. Not exactly a concern for any of us.

I’m not sure how your wife has proven the extended longevity of fans through the non-stop operation. Any such theory needs extensive scientific study before conclusion. Additionally, what is the saving after power consumption? Until then, I’ll go by the proven idea that any mechanical device is subject to wear and tear with use. Longer the use, more the wear. It even applies to electronic devices, which may be just passive displays. The other extreme is the disuse. Business/critical situations do go over economy for other important considerations. They are not to be generalized with normal uses.

The second issue is one that my company has debated for years with no solution. Does keeping a motorized device [hard drives, fans, etc] running full time last longer than turning it off every day? And then endure the high mechanical demand of restarting and coming to speed?

We found that it works both ways. We have thousands of motored devices, not just computers, and found some will last longer if allowed to run 24/7. Unfortunately, the tests were not conclusive. We never did get an answer.

[as a side note, I mentioned this to my wife who insists on running our room fans 24/7, only switching to low at night. She has proven to me they last longer]

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Have a great day!