Why a prong?
I remember back in the 80's and early 90's that a choke chain was the way to go. Then I moved away from home and didn't have a dog again until 5 years ago. Sometime between the mid-90's and mid-00's the choke chain fell out of favour because it could be dangerous to the dog. I always heard/thought the same about prong collars.
Our 5.5 year old uses a martingale because she needs the tightening the chain part provides. If we use a straight nylon collar she pulls like the devil on leash walks and with the martingale she's much better. But when we bought the martingale, the local pet store owner looked down even on that and talked badly about prongs, saying they were only for very aggressive dogs with bad owners.
But on this site, and from what I've seen at the few meetings I've been to with other GSD owners, prongs are very popular.
Why do you use a prong? What are the benefits it provides? How do you use it correctly? Are there any down-sides? Can it hurt the dog? I'm a total newbie to it so any comments, either for or against, are welcome!