From another thread it appears that WD Live uses very little power. Longevity wise, is it better to leave it on 24/7 (assuming we take a usb disk out of the equation) or turn it off when not in use?
You’re asking if the unit itself will last longer if it’s left on?
Given that it’s a totally solid state device, with no moving parts, I’d assume it doesn’t matter much either way. While some devices (like light bulbs) tend to burn out when the power first surges through them, the Live uses a transformer so this wouldn’t be an issue either. Since even older tube type TVs tend to last for decades, it’s likely the Live will outlive you (or at least outlive the technology).
From a “green” perspective it’s probably best to not power the transformer (that’s what I do – I plug the Live into a Smart Strip which unpowers the whole thing when the TV turns off) but we’re probably talking very little in terms of money. Actually, my far bigger concern in Florida is the lightning strikes, so I mostly completely unplug things during storms (about the only way you can truly protect electrical devices). But for you? I’d leave it on if it’s most convenient (but that’s just IMHO).