The manufacturers of my SS disc player and SS preamps say to leave them on all the time (one of the preamps doesn't even have an on/off switch). My tubed CD player has a convenient switch that turns off only the analoge (tube) power while leaving the digital section powered up. Since it has only two tubes, I often leave both analoge and digital powered up all weekend since I listen at various times. My SS Class A power amps (300wpc) get very hot. Fortunately, there is a bias switch that can be used to lower the power and the heat. Although I generally turn the amps on only when I want to listen, having the bias switch gives me the option to bias down and leave them on for longer periods of time (although they still get warm). I have thought about switching to SS amps that can be left on all the time, but there are only a couple of A/B designs I would consider switching to. When I had tubed preamps, I sometimes considered the trade off between using NOS tubes and turning the preamp on and off, or running less expensive tubes but leaving the preamp powered up all the time.
Do you leave your components on 24/7?
Lately I've been leaving my components on all the time, on the assumption that a) they'll be ready when I want to listen, and b) the on/off cycle ages the equipment (tubes, anyway) faster than leaving everything on. Is the latter a reasonable assumption?