The low jab intercept is one of many "level change and attack" possibilities, conceptually similar to the clinch entry in that respect. It's a great way to surprise your opponent and change the game in your favor, and can be a solid conditioned response against an unexpected barrage of punches.
In the images below the defender uses a punch for the high cross. We'd generally prefer to use a palm rather than a punch in self defense, as the chances of breaking your hand on your opponent's head are high.
See more self defense techniques.