power supply

How often do we have to turn off our equipment such as power amp , pre amp. cd player , power conditioner ......? Can we leave them on for days while listening on and off or do we have to turn them off after every session of listening? As a general rule the more the systems are left on the better the sound , so what is your idea on this issue ?
I have found it to be particularly important to keep my SS equipment powered on for this reason; when powered off the cable connections in the system (particularly the speakers cables) will oxidize a small amount. Unless the cables are disconnected and cleaned periodically (cleaning is a good idea anyway), the build-up in the connection can materially effect the quality of sound from the system overall. In my case, I have designed all rooms with conduit and wiring chases to virtually eliminate the wires from view, but in so doing I have made it more difficult to get to the cables for maintenance or change-out. As a result, it makes sense for me to keep the SS equipment on. The one major drawback to doing that though is that the system will become more magnetically biased which can be addressed through the use of de-mag products from companies like Ayre and Denson.
Many quality preamps have been designed to remain powered on, in some fashion. I would check on CD, etc, players as many have standby features. I always liked to have mine playing well before I listened. However, exceptional power conditioning for my CD player has made such a dramatic difference to sound quality I'm now ok with the sound from standby, and haven't felt the need to further evaluate. The conditioning resulted in spectacular improvement; far more than any warm up. With SS amps manufacturers often have a recommendation. Don't forget all items that heat up also wear out/degrade over time.