Ideally, a dog shows a lot of restraint when acting defensively. In many situations a dog may accomplish what is needed by just a posture and then escalating accordingly to a growl, snarl, snap at the air, a "hit" where the dog hits a competitor with his teeth but does not injure, and then escalating levels of bites that will cause injury before an all-out fight or attack.
Particularly, during resource guarding and normal dominance related conflicts we typically see appropriate restraint and the minimal amount of aggression to resolve the conflicts. When there is obviously much more aggression than would be necessary for a situation we would say the dog is also "skipping steps in the aggression cycle".
Skipping steps in the aggression cycle, in rare cases, can be the result of intense human punishment for early steps in the cycle, particularly growling.
Usually, genetics is the main culprit and the behavior can be found in bloodlines of many breeds that are otherwise not known for overly aggressive behavior but were haphazardly bred.
In other bloodlines, the behavior was an intentionally selected for trait that gave an advantage to certain working dogs, terriers, and fighting breeds that needed the advantage of a quick bite to excel at their tasks. Skipping steps in the aggression cycle can also be associated with not responding to signals of surrender and submission after the onset of aggression.