I think of a handgun bullet wound as a combination of blunt trauma and penetrating wound.
The temporary cavity equates to blunt trauma. It causes pain, bruising, and may, if the right organs are involved, cause some wounding. Think of it as a punch. It won't generally cause any significant injury unless certain organs are involved. The spleen, for example, isn't very elastic and can be ruptured by blunt trauma. The liver is the same.
The penetrating wound goes deep and is likely to cause serious injury because when you start poking holes all the way, or at least most of the way through a human body, it's likely something important will be damaged. It may or may not cause immediate pain, but if you die or become physically incapacitated, the penetration aspect of the bullet wound is probably what caused it.
You want both. It's pretty obvious why you want penetration--if physical incapacitation is necessary that's the way you're going to get it. Also, the penetrating aspect of the wound is a big part of why guns are so feared.
But you also want the blunt trauma because it immediately lets the attacker know that an injury has taken place. It's of no value if the attacker bleeds out 5 minutes after killing you. Most handgun "stops" are due to the attacker giving up and their understanding that they have been shot is an important factor in that respect.
In my opinion, the "notification" aspect of the temporary cavity is likely the biggest benefit of expansion in handgun rounds. Good expansion causes a bigger temporary stretch cavity. The larger the stretch cavity is, the stronger the "punch" that the attacker feels and the more likely they are to interpret the injury as serious and give up.
The temporary cavity equates to blunt trauma. It causes pain, bruising, and may, if the right organs are involved, cause some wounding. Think of it as a punch. It won't generally cause any significant injury unless certain organs are involved. The spleen, for example, isn't very elastic and can be ruptured by blunt trauma. The liver is the same.
The penetrating wound goes deep and is likely to cause serious injury because when you start poking holes all the way, or at least most of the way through a human body, it's likely something important will be damaged. It may or may not cause immediate pain, but if you die or become physically incapacitated, the penetration aspect of the bullet wound is probably what caused it.
You want both. It's pretty obvious why you want penetration--if physical incapacitation is necessary that's the way you're going to get it. Also, the penetrating aspect of the wound is a big part of why guns are so feared.
But you also want the blunt trauma because it immediately lets the attacker know that an injury has taken place. It's of no value if the attacker bleeds out 5 minutes after killing you. Most handgun "stops" are due to the attacker giving up and their understanding that they have been shot is an important factor in that respect.
In my opinion, the "notification" aspect of the temporary cavity is likely the biggest benefit of expansion in handgun rounds. Good expansion causes a bigger temporary stretch cavity. The larger the stretch cavity is, the stronger the "punch" that the attacker feels and the more likely they are to interpret the injury as serious and give up.