It just occurred to me, after reading the above replies, all of which I found very interesting, that if I changed "engine" (or "locomotive") to "motorized unit," it would take me another hour to run everything.
Motorized units would include trollies, gang cars, tie ejector cars, borrough cranes, and the like, as well as the engines/locomotives.
Everything that has a motor is even more expansive.
I believe it is a good idea to run everything that has a motor at least once in a while, maybe at least once every 6 months. Everything that has a motor would also include accessories.
Since I have a lot of accessories on my layout and more in storage, that would take at least several more hours for me to run every accessory for 2 minutes, especially since those in storage would need to be hooked up to a transformer to run them.
There is one accessory that I run for a few seconds almost every day: the #38 water tower with the water pump and real distilled water. Since I've done that, it has now worked like a charm for over 5 years. Before I did that, the water pump in it would stop working every month or two.
Do you agree that everything that has a motor should be run periodically and regularly to keep them in good working order?
If so, how often?