Too cold? To far away in case of zombie attack? Might fall off? Seriously though:
The way I understand it, the only time you do that is when you are going to adjust your carb at wide open throttle. I think what he meant was the manufacturer states that the saw can safely idle for at least ten minutes. That should be plenty for anything, but I doubt I'd be able to wait that long myself... I let it idle a short while, until the idle has stabilized and the chain is perfectly still, then check throttle response and start cutting. It just seems when it is working properly, it is also warmed up enough.