As usual there's no real consensus of opinion here other than probably not leaving it on unless you nearby to attend to it if something bad does start to happen. If I'm playing on and off throughout the day mine tend to stay on. Both the tube and the SS amp. I may be putting a few hours on the tubes but surely no more than if I was gigging or recording that day. I've always tended to leave SS devices running since IME they tend to fail far more often when powered up than when left on. My stereo gear has stayed on like that for years with no problems at all. I'm not sure this is a right way or wrong way thing. It seems to me like more of a your way or my way kind of thing.