Liver punches are pretty painful and should not be done in boxing or at anytime because getting punched in the liver is really painful and can cause life threatening problems.
Liver punches can incapacitate a person at once which brings them down so if you need to do a liver punch during an attack by someone then punching the attacker in the liver can incapacitate that person and stop the attack.
However if possible try to get away from the person before engaging in a fight with them.
If you're boxing or just playing around then doing a Liver punch should never be done to the person you're boxing or playing around with as it can potentially be fatal.