I don't think I've ever had a printer that has said not to leave it powered on.
I didn't see this in my Epson or Mutoh manual, nor did the setup/tech mention it—I'd think it would be front and center if it were that critical. 10-color mode is the only time the Epson manual specifically talks about being left on.
I am onboard with leaving the S80600 on overnight if you are in 10-color mode with white ink—I can confirm things go smoother that way. Shake that white ink every day too.
Maybe folks are assuming there's more magic happening when the machine is asleep than I am. The only thing I've observed the machine does while asleep in 9-color mode is keep the board/cpu fans spun up*, and occasionally (not even once a night, if you're checking) running a cleaning cycle. There are
no ink circulations done or even available in 9-color mode, only cleans.
My concern with leaving it on when not in use, is that I get a power outage, or some other gremlin appears that I'm not there to resolve it. My Mutoh did occasionally have a vacuum or wicking issue that would
only show up while in sleep mode... so that might play a factor in my bias. I have no problem running the 80600 unattended occasionally—running a roll overnight.
I get several cleaning cycles in a regular 8-10 hour day while my machine is on, so for me the other fears outweight the chance of squeezing in more cleans—It's sure not about saving dollars on ink and electricity. If I only had one job a week, or every couple weeks, leaving it on to do it's thing would probably make sense, but I'm running something 5-7 days a week, 365 days a year.
I don't think there's anything harmful about leaving your Surecolor on 24/7, I just choose to weigh the pro's and con's a little differently than most folks (apparently.)
*Regarding the fans that stay on, I had hoped SignMeUp would be willing to offer up their 3DPrint files
mentioned in this post. The psychological effect of not hearing them while the machine is asleep
might be enough to have me join the majority... ;p