Personally I prefer to keep it unpowered, unless we pass defcon 1. :) It could be interesting to have a tube outside powered 24/7 because we would be more sensitive to small variations. indoors I think it's less relevant. but it can be interesting to keep long records taken from time to time as a reference. but otherwise it is no problem to keep 600+ running 24/7, it is made for that.
Mastery is acquired by studying, with it everything becomes simple
Yes,leaving it on should be fine. Someone recently calculated it should last for billions of clicks. Check recent threads. I was just being cautious,and hoping it would be usable for a great many years.