Leave it on?

As you can see from all these replies very equipment specific. I don't believe Paul was issuing a blanket leave it on but rather if you have standy mode then use it as it keeps the electronics consuming little power but ready to perform quickly at peak efficiency. 

I keep SS gear on all the time unless on vacation or a storm.  
 

How long will you keep your new gear? 1 to 20 years as I am an audiophile 🤓.  Just don’t know. 
How do you feel about global warming? Really not a thing you know.  Current thinking is coming around to this thought. If you haven’t studied it, wait till you learn that we can’t even measure the Earth’s temperature accurately. Never have, never will. Our instruments, we humans, and our methods are flawed.  Always will be. 
How confident are you leaving other appliances on all day and night? Like my refrigerator? HVAC? Some lights? Water heater? I think you get the point. 
How would you feel if your house burnt down? Not good.  What does this have to do with the topic?  I think interjecting fear on this topic is not helpful. All of our homes have live 120 V outlets and electricity networked throughout the home. Fires do happen and that is certainly a possibility in most any home.   However, suggesting that leaving on a streamer, dac, power conditioner or amplifier  is more likely to cause a fire is really not serious.    
 

In most cases this is just picking nits. Well-designed gear that is relatively low in idle power draw (preamps, class D / G / H amps) should have NO problem either way. Do what you like. Gear that is high in constant power draw, are therefore heat dissipation - tube power amps, class A and high bias AB solid state power amps - should really be kept OFF when not in use. In my experience, hotter components are also more likely to sound good quickly after warmup - simply because they hit thermal equlibrium quicker. SS is always slower to warm up than tubes.

@grannyring ”What does this have to do with the topic?”

l think you missed the point. My point was not leaving electrical devices on unnecessarily. 
Refrigerators left on yes, the nature of the beast. Every electrical appliance is a risk factor. In London a refrigerator caused a fire in a housing complex, Grenfell Tower. 70 lives lost that night.y

Yes again with global warming, arguably self destruction with the jury more in than out. That was only part of the debate regarding wasted power, it’s not all cleanly generated like wind or hydro-electric.

@mulveling Good points posted on what you believe “should be kept OFF” 👍

@mylogic I understand your point. I suppose life with our technology and conveniences comes with risk.   More risk than life before them some 100-150 years ago? Different risks for sure and obviously less overall.  I just don’t see the added risk of keeping your Class D amplifier on. Class A SS amps don’t all run hot today. Valvet is one example. I would not leave tube gear on 24/7.