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.