By all means, keep your equipment on 24/7. Everything will sound better that way..
Remember that recording studios and broadcast stations keep everything they have on 24/7 so they'll aways be able to get the maximum performance from it whenever they need it. This includes the remote trucks too. And as pointed out, some equipment is designed for it, or requires it, such as class-a and tube equipment, and power conditioners and UPSes.
If you power your equipment on and off it really won't be ready to give you the sound you appreciate sometimes for days after you turn it on, and you really don't spend that much money doing it. And I've found that my equipment lasts so much longer.
I have 6 amps (Anthem, Denon, Sony), 5 Sonos Connects, a Parasound AM/FM tuner, a DAC, a Teac cd recorder, an Arcom cd player, a Revox RtoR, and a Carver preamp that are all on 24/7. Some of them are plugged into sine-wave UPSes, and my main stereo stack is on a Furman power conditioner. Everything is on 24/7.
I also have a home data center with 4 servers, 2 switches, a router, 4 desktop boxes, and a wide-screen monitor, These are also on 24/7.
All told I figured out this costs me around $50 per month.