"Sorry, holocaust survivor. It wouldn't serve a purpose to society to jail someone who knowingly played a small part in the murder of your entire family. We have to think of our budget and whether or not it will rehabilitate him."
It depends on what you think people should be incarcerated for. If you think that it's done to protect society/rehabilitate the criminal then there is absolutely zero point.
If you think it should be so that people can get revenge on the people who wronged them, then there is absolutely a point.
I personally wouldn't want to be part of a system that thinks imprisoning people based on a personal sense of satisfaction is a good idea, but c'est la vie.
EDIT:
Some one else says above that we should do it for the sake of the rules existing. That would be a kinda cart-before-horse scenario, wouldn't it? The reason we have laws is for the safety of society, not simply for the sake of it.