Leave it on?

There is no one size fits all answer. Some equipments turn themselves off after being inactive for a certain period of time (Marantz AV-10), others are just impractical (Class A amplifiers). On the other hand some can stay on and ready without causing any damage to themselves or the environment (Class D amplifiers, DACs etc). Some manufacturers recommend it. Just make sure the equipment is in dark mode (display off), otherwise you might cause display burn in where the characters stick to the display like a watermark even without power (not good for resale value). 

@spenav + 1

I leave my Innous streamer, Technics TT, and PS Audio phono pre, DAC, and power amp ON all of the time (except during thunderstorms). When not in use, I turn off my LTA preamp, and 40-year-old Teac R2R and dbx noise reduction unit OFF.

@maprik From the PS Audio BHK250 user manual, “We recommend leaving the rear panel power switch active at all times but placing the unit in its standby mode when listening has been finished. Standby can be activated by pressing the front panel PS Audio logo button, located on the upper left-hand corner of the BHK Signature front panel. When the logo standby button is not lit, the amplifier is in standby mode, and the vacuum tubes are turned off. Standby mode keeps the solid-state circuitry of the amplifier in a reduced power mode, maintaining excellent performance benefits while consuming little power.”

There is no issue with tube amps--they should be turned off when not in use because all tube filaments have a limited life and tube amps warm up fairly quickly.  With solid state, the answer is a bit more complicated because life of transistors are not as significantly shortened by being in a quiet on condition as compared to tubes, and solid state gear does take longer to warm p and sound its best.  But considering power consumption and safety, one may still prefer turning it off when not in use.  Another thing to consider is electrical storms or other times when power is acting up--if you are not home to shut off gear, you will be exposing it to dangerous conditions that may damage electronics that remains on and even the speakers from resulting excessively loud pops. 

The only thing I leave on all the time is my streamer because that is what the manufacturer recommends (they say it take a very long time for capacitors to fully charge and reform if the gear is shut off).  The rest of my gear is tube based and there is no question that it is better to shut off completely.

I contacted Legacy Audio about leaving my Focus XD’s internal amps on or off, Ed said to leave them on all the time. Aurender recommends leaving the streamer on, so I do. Denafrips recommends just leaving my DAC and DDC on. (Neither has an on off button, the DAC does have standby though.) My Legacy Wavelet is on all the time. My Coda s5.5 amp  has standby so I put it in standby when done, however when I plan to listen I try to turn it on at least 30 minutes before hand. Of course when we leave for FL in the winter everything is off and covered for 5 months. 

In our home theater most everything is on all the time except for the Television, it’s on standby. (Sony) The Yamaha HT receiver turns itself off through HDMI e/Arc when the TV goes off.