Why all the controversy? Check with the manufacturer. Plinius told me to to leave it on all the time for maximum life since cycling on and off causes more wear and tear than just leaving it on and since it is a Class AB SS amp it draws very little current when not playing. My amp is 18 years old and counting (and I bought it very slightly used from a high end dealer who told me I don't "have to" leave it on, which suggests it is better to leave it on). I will say that even though it is always on, it seems to sound a little better after playing for a while. In fact, they moved the power switch to the back on the model that replaced mine (which is almost the exact same amp internally) to strongly suggest leaving it on. My phono stage and all those made by Sutherland have no power switch. so with that is isn't even a point of discussion. Same with Rega tables - they either turn or not. So everything is always on! If I was burning out expensive tubes I would probably turn them off and suffer through the warm up period.
Interestingly enough, I was told the same thing from an Apple technical guy about my MacBook Air which I view through a 24" monitor. I use it as a server with a wireless keyboard and mouse. He said leave it on and plugged in with the lid shut. I think the less start up cycles with pretty much anything electronic, the better, when it is feasible.