What are dog shock collars used for?

I have a Brittany and indeed the collar does work. While we have a 24 acre spread bording a very nice spring fed creek and lots of field and woods, our dog loves to cross the road in front of our place. She is attracted to kids especially and will forget all training and run towards them almost at any cost. Of course this is very dangerous as we do have traffic on our road. I use a shock collar that is both waterproof and has sound. I trained her to come when I call her without the collar and then she knows the command. I first used a mild shock and a little heavier shock if she chose to ignore me if the temptation was strong. After awhile she learned that when she has the collar on she is to mind and does. I don't have to use the shock anymore as the sound works magic. She does not mind all that well if she does not have the collar on so I did something wrong I am sure?