I  inquired about this exact same thing, when I got my Fireface 802 about 18 months ago.  I was told by support, that it didn't matter either way.  If I decided to power it down every time, or leave it running 24/7, it didn't matter overall to the units health.  I replied with my concern about heat, degradation of the components etc and they replied back again, saying all would be ok.

For what it is worth, I have mine powered up 24/7 and have since summer of 2016.  Really curious if what support told me was right though and what others are doing.  I would hate for my $3,000 investment to prematurely burn up on me.

:-)    Yes, when necessary.

But shutting down gear, if it is to be done, includes computer, powered speakers, satellite hard drive, musical amps; not difficult, nor tedious, but rather it has raise a question for me as to whether 'tis better to remain powered up than to shut off, then on, off, on, perhaps several times during a single day.  I'm not clear, objectively, about what the best way to care for the gear is.

I thought perhaps RME had a clear piece of advice on this.