Reliabilty, Keeping Equipment Powered on or off?


I generally keep my system components powered on because the system does not have to "warm-up" when I sit down for a listen. I do know that reliability is usually calculated by POH (power on hours) however this calculation IMHO is a broad brush stroke. I do power down certain components that are not required to be left on to sound their best, such as a Luxman T-117 tuner and Wadia 171i Dock . However, my Krell IA, with the volume turned all the way down runs pretty hot, so hot you can't leave your hand on it. When turning the volume up on the Krell to reproduce the live event sound level, you can fry an egg on it, so I can only guess the Krell was designed to handle this kind of heat? However, back to the other components, such as DAC, SACDP, Headphone Amp, etc. Is keeping everything turned on asking for trouble or is leaving it on best to prevent thermal expansion and contraction which may be detrimental?
grm
Do /you/ notice a difference in sound quality if they are left on? I would leave them off. I assume the DAC and CD have standby modes.
This subject has been discussed previously in the forum, but does get resurrected every so often. Personally, my view is "it depends". Putting aside the added electrical cost, minimal or not, I completely power down all of my components when not in use. Meaning, I do not care for "standby" mode for hours on end until I'm ready to listen. The caveat here is that I power down in cases where I know the next listening (or watching as my video is connected to the same power source) opportunity will not be for another 24 hours or so. If, one the other hand, I listen/watch something in the early AM and take a lunch break with the intention of listening/viewing an hour or two later, I would leave the components on. 

While I have solid state equipment, other considerations may need to be accounted for in the case of tubes or other circumstances. I do not know, but I'm reasonably certain others will chime in.

I simply do not buy into the notion of "warming up" my equipment. That said, I do know that electronics of any kind should not be exposed to "extremes". For instance, if for whatever reason you have your amp in your car and it happens to be the dead of winter, you wouldn't want to take it out the car and immediately set it up at your listening location, turn it on, etc. So the caveat here is that equipment remains at normal room temperature. 
You can turn off the DAC, SACDP, Headphone Amp when not in use, as they will warm up quickly before a listening session. 
Buy a low dB computer type fan for the Kell and leave it powered up. It takes a few hours for an amp like that to warm up for optimum performance.