Until my current job I've never left the helo without someone at the controls, then again when I flew for the Marines we always had two pilots so someone was always at the controls when the engines were on.
Now that I'm flying civilian I leave the helo at flight idle and exit the aircraft almost every flight because my job requires me to get out to collect samples. It does have friction locks on the cyclic and a lock on the collective. Most of the time I'm only out of the helo for a couple of minutes and usually within 100 ft of it.