tempted to turn on and leave on all day. Instead of powering up and down many times.
Correct answer depends entirely on what you mean by "many times". If you mean many times a day, the greatest most intense stress is the thermal expansion going from off to on. This is why some designers like Herron incorporate slow warmup circuits. Greatly extends tube life.
But if "many times" means one time a day? Well then look at it this way. Let's pick some arbitrary numbers and say tube life just sitting idle is 5000 hours. At idle. Playing music uses more power, tubes get hotter, wear faster. Let's say you crank that thing full blast all the time. Tubes last 3000 hours. Just throwing numbers out to get you thinking in terms life and wear. Though these are probably in the ballpark.
Okay so now every time you turn them on from cold, that flip of the switch is something like at least an hour of running idle. So if you are turning it on and off 3 or 4 times a day then probably better off just leave it on. And that's how that works.
