Question about Audiologic 2400 DAC

I recently purchased one of these and had a quick question regarding it's operation. Should this unit be turned "off" when not in use? The switch is in the back and this would intuitively lead me to think not, but possessing tubes, you'd also think it should be turned off?

The light for the LCD display remains on as long as it's plugged in. Any owners willing to chime in? Thanks!
I keep mine on. I spoke to Jerry Ozment (the designer and maker), and he agreed.
The tubes are low power and should last a long time.
keep it on, my tubes have lasted 2-3 years while remaining on.