you must have a huge backyard...
as others have already said, when you have your e-collar conditioned dog running off leash it is reasonable to me. however, you should really see a rapid decline of its use!
by the way, it took me quite some time carrying one (with empty batteries) until I realised that I - not the dog - had begun to need that thing for psychological reasons, and I wouldn't think of myself as control freak.