I would go by whatever the manufacturer recommends. Generally, I leave most of my gear "on" or in "standby". If I owned a Class A solid state or tube amp, I'd likely turn it off in the summer to keep from heating up the room too much but might leave them on in the winter. As noted, thermal cycling is what kills electronics or them getting too hot from the buildup of dust - so every once in a blue moon, clean your gear out carefully - or cover up the ventilation holes and slots when not in use if they are turned off. Streamers, your Wi-Fi router, and modem need to be rebooted every once in a while, to maintain a good connection and clear out any "cobwebs". I do mine about once a month.
Leave it on?
I just listened to Paul McGowan explain that turning SS equipment on and off degrades the capacitors from the tiny power surge and that leaving SS equipment on ALL THE TIME is best. What do you do?