I leave my primary systems on 24/7 (3 of them in rooms I use each day), except for the tube components (preamps). I have several "auxiliary" systems in rooms that don't get much use, and those systems are off except when I'm in the room.
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?