Don't think it makes that much difference.
However, I had a massive spike on my mains supply the other day, while I was useing my gear.
Knoocked out a fair bit, and I had to power down everything and restart.
If you get a probelm wuth your supply while your away, and the thing is getting something it rather not like, it could do a great deal of damage. I would rather be around a item at the time to shut everything off to protect it.
I would power it down, that's why they have memory batteries inside, to keep the data. Almost all have at least 5 years of life, having the unit on, might extend that about a year if your lucky.
Better to backup your data vai sysex now again too.
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The Sonic Energy Authority - a sound investment
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The Sonic Energy Authority - a sound investment