Yes, leaving on will reduce life. However, if the SN3 at idle is not very warm so not too much effect.
Turing it on/off is fine. It can ultimately stress the rear mains fuse. Caps, transistors etc are fine.
Also never powering it will reduce life. If caps do not get used the dielectric does not form.
My advice is use and enjoy.
Once run in it’ll come on song in an hour or so after a power down.
Some listeners are more sensitive, Roy G and Paul S did not like turning their active systems off.
I leave mine on 24/7