In the work force, people who have been at their jobs for any length of time, obviously know their job pretty well. Whether it is cooking french fries at Mcdonalds or working for an accounting firm, you would know your job pretty well after a while. Even in those instances, they do not let just fire all of the managers, and let you pick up your check under the door every friday. Someone is still there to constantly oversee the operation that it is functioning properly. Without that, the organization would fall apart quickly.
Dog training is no different.
The reason that the ecollar is kept on when moving outdoors, is because as you step outside the house a lot of factors enter into the picture that you have no control of. Loose dogs, cats, kids on bikes, trucks driving by with dogs in the back and people playing frisbee are just a few. To correct the dog, the time that it takes you to get back there, slows learning tremendously. Also, it is very hard to not get emotional about it because you want it to cease immediately, thus further creating another bad habit of yelling at the dog. Another thing that happens is when you are finally able to correct the dog, it has moved, and gotten away with a fair distance before the correction can be applied.