What Would Be the Reasoning Behind Leaving Class D Amps On?

I think my Marantz Ruby integrated sounds better if it is just permanently left on.  I'm a bit of a tubehead, but I've had 2 other Class D amps and I recall them sounding better left on. 

I've seen a handful of manufacturers that even recommend their Class D amps be left on--e.g. PS Audio, etc. 

In addition to the potential improvement in sound quality, I suppose keeping caps and things on might be easier on them too.

Do you agree?  Do you know why this may be true or at least the theory behind it?  

Thank you in advance!  I'm super curious about this stuff.