One advantage of enforcing laws is that it leads to greater stability and order in a society. I have attached a link below on the "broken windows" thesis, which argues that the toleration of petty crime can lead to the break down of society.
In a society, it is important for people to believe that the laws will be enforced. People need to feel that others in their society will be forced to follow the rules that are supposed to be followed. This will make people feel better about following the rules themselves.
Think about this in the context of a school. If the administration lets some people get away with breaking rules, other people will be upset. They will feel like suckers for following the rules. This will lead to more and more people breaking the rules and the "society" will fall apart.
People in society need to feel that rules are being enforced in order for society to remain stable. That is one reason why enforcing laws is so important.