Do I NEVER shut it off…?

No need to leave amps on all the time, just turn them on for awhile before you are going to listen so they can warm up. How long that is you'll have to find out or take the advice of other owners.

I  have a pair of Class A amps that use up 300 W each when not putting out any sound. Keeping them on all the time would make the electric meter spin like a kid's pinwheel toy and would also turn any room they were into into a sauna in summer.

Like I said, it depends on the amp. Not a black and white issue people (as few are...).

I have all Ayre electronics which provide a trickle charge when "off". I don't hear a change from when I turn it "on" to an hour later, however, MCarbon may very well be right.....so I'll leave it on for a couple of weeks, turn it off and listen again the next day.  Thanks for the tip.

The Ayre VX-R benefited from being left on. Possibly due to the Billet chassis cooling combined w On Semiconductor thermal trac output devices. The VX-R Twenty, sounded fantastic 20 minutes out of Ayre standby.

I agree with @sokogear. I use a Plinius pre and amp and my rig is always on unless I go on vacation. I always power everything down then just because of potential lightning storms. My rig has run this way for years. The way I look at it, cooling and re-warming is like bending a piece of metal, eventually it will break. I don't know if there is any validity to that hypothesis but that's what I do.