Leaving your hifi powered on
I dont subscribe to theory that hifi should, ideally, be left on. No particular reason other than a habit of just switching things off at the end of a day. I have, on occasions left it on but probably didnt notice any change either way.
I had a look at some electrical components for a little project and noticed manufacturers quoting a life span for some, measured in thousands of hours. I would assume that these are cautious ratings, probably further complicated by perhaps using maximum component stress figures which, in real world, conditions, is not really relevant.
I have no idea if this finite life time of a component means it will fail suddenly but I somehow doubt it. More likely, the part will produce less and less of its initial quota and slowly deteriorate, at least with items such as power supply capacitors. This will probably not be noticeable in a week to week or even month to month usage but may well would be if say a new, unused version of your hifi component would be compared side by side after a couple of years or more. I am not talking about total failure and also exclude tube products from this as they certainly have a limited life span.
There is the other argument that switching things off and on repeatedly may cause more stress to the circuit and could result in failure before individual parts reach the end of their useful lifes. I dont think, as far as I know, anybody has made any useful research in that respect which would show that this is indeed the case though I may well be wrong.
I'm not going to change my habits. Electricity costs money, I dont notice much difference by leaving things on and its my little bit to save the polar bear.
Perhaps you think differently ...