I guess it depends on what you mean by "not using it" and for how long. For example, if you're going to take it off for several hours and it won't be on the charger, you might as well turn it off to save the battery, but otherwise I'd say to just leave it. I've had mine since launch day and in the past month I've only turned it off for a couple of resets, and I put it in power reserve mode for the first time last week. I charge it nightly, and have only had one day where I was "worried" about the battery.