Heat kills is true but as long as components are operating below their rated temperature they should be fine. My Pass Labs mono amps, in fact most Pass amps operate at 20C above ambient. I've used my low cost laser thermometer to confirm that. They will last a few decades operating at that temperature. And I have found that they sound better after being on for a few days. The problem is my conservative midwestern upbringing prevents me from leaving my amps on if I am not listening to the music. Once in a while on cold winter days I might leave them on overnight. And in reality it's only going to add a couple of dollars to the power bill leaving them on for a few days. It's still hard for me to do. Growing up, if a room was empty there better not be a light on.
I'd be reticent to turn my high powered gear on/off a couple of times a day everyday. The thermal cycling for hot running gear could be detrimental. Maybe don't leave it on overnight but turn it on in the morning and leave it on for the day. Cut the thermal cycling in half.
Here's a cool story: I worked out at a large railroad yard the summer of 1976, just before starting college mowing the grass, trimming trees, unloading wrecked railroad cars and other odd jobs. One day I was mowing and stopped at a shack that was across from the "hump". The hump, or hill was used as a gravity feed to build the trains. The railroad cars would be cataloged, roll down the hill and were then fed to various spurs to build the trains going to their new destinations. This shack was a radar shack. It's sole purpose was to read the speed of the railroad cars going down the hill and apply brakes to slow them down as needed.
The railroad by then had seen their heyday. Most of the technology being used there was from the 1940s and 1950s. I walked into this shack and I saw a room to my left full of wet cells. On down was another large room and a man sitting at a desk. This room had two large banks of vacuum tubes, one on the left and one on the right. These were several refrigerator sized cabinets full of vacuum tubes. At the end of the room were some windows with a view of the hump and one small meter reading out MPH. He explained to me the purpose of this shack. It was a large vacuum tube powered analog computer whose sole function was to read the speed and apply the brakes. It was amazing.
I commented to him that with hundreds of tubes in these cabinets he must be busy changing them out all of the time. He said that he hadn't had to change a tube in 11 years. I was amazed. He said it is never turned off.
