I have unplugged laptops to put in the safe at the office for years at a time.
Why? We have systems we developed years ago and to make sure we can access them we have usually 2 laptops that go into storage along with backup discs for that project. If any updates are called for we can pull one from storage, apply power and start work within the hour.
So far, this has worked fine. Leaving them attached to power would however leave them exposed to power issues.
Bob
Going abroad for 2 mos. Leaving iMac behind. Best to unplug everything--including backup battery pack, etc.?
Or no problem to keep it plugged in?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic