There were historical magical wars in my fictional realm and the damage done to certain areas so severe the land became barren. Then there was the tremendous loss of life because of the wars and their after effects. Nobody wants this again so the rules were brought in to control magical beings. It was felt (and still is at the time of my novels) that this kind of control would ensure wars could not erupt. (Many of them did out of feuds).
So, especially if you write fantasy and/or science fiction, what counts as a crime in your world? How is it punished? Who carries out the punishment? What are the reasons for the laws on your world governing this aspect of life?