Some trainers use aversive collars to train “difficult” dogs with correction or punishment. These collars rely on physical discomfort or even pain to teach the dog what not to do. They suppress the unwanted behavior, but they don’t teach him what the proper behavior is. At best, they are unpleasant for your dog, and at worst, they may cause your dog to act aggressively and even bite you.
More humane collars and good obedience training should make it unnecessary to resort to this aversive collar.