This is and has been a contentious topic of discussion for year hear on Audiogon. The issues have been:
1. sound quality of equipment when left on all the time vs turning the equipment on for an hour or so before serious listening.
2. Energy usage and wasting energy.
3. Summer use and the amps (typically) are space heaters (again wasting energy).
For me, I know that anything left on continuously will degrade the life of components. Equipment with standby modes, reduce this dramatically. This allows for devices to have the capacitors charged, but the bias isn't at maximum.
From a safety point of view, equipment left full on (not in standby mode) is not really a good idea ever. Refrigerators, notwithstanding, because you really don't have a choice. But anything else, it not a good idea.
From a sound perspective, on my equipment, could not distinguish any difference in sound from my equipment being left on or turning it on an hour before listening.
For tubed equipment, there is no way on Earth I would leave it on continuously. Most manufacturers tell you the life of the tubes, If you leave it on, well, that life is dramatically reduced. No way to get around that, unless there is a standby mode that has those tubes turned off.
If you have the money to replace tubes often, then that is your choice.
But, I often see opinions here based on Sound quality and safety, and Safety should always come first.
This is the "it can't happen to me" logic. It always happens to someone else, but not me. Until you come home to a burned house, or you listened to some well intentioned but totally ignorant person and eliminated your ground by lifting the ground to eliminate some noise, and then a fault happens and someone is hurt.
Safety first.
I turn my equipment on about an hour before listening. I unplug all my audio equipment when I leave for a few days or more.
enjoy, but be aware, use common sense and be safe.
