leave power on?

I agree with Jax2. Tubes dont take long to warm up and sound good after an hour or so. There is no need to leave tube stuff on when not in use.

Solidstate gear is a little different and in my experience sounds better after quite a long period of being left on. The latest gear after being burnt in doesnt suffer as much as some of the older stuff though.

Save energy where you can. As the flood water washes your house away followed by the desert sands covering the plot where it stood, try explaining you used to leave your hifi on 24/7 because you got sweeter highs and slightly more separation!

I've heard that one should never leave tube amps on 24/7 because its a fire hazard, almost like leaving an iron on. My tube amps definitely sound better after at least 30 minutes of warm up though.

What Jax2 said X 4!

Tubes: turn them off
Solid state: leave it on

SIMPLE

With tube equipment it simply has to do with the cost of retubing. Better to turn off tube equipment and warm it up for a short while prior to listening, unless you will be doing a lot of listening during the course of two or three days, such as weekends, where the thermal issues associated with turning off and on are probably harder on the tubes than leaving the unit on for such a period. This last recommendation comes from one of the people at ARC who provides information over the phone.