Why is it important for laws to be written down?

Written laws are important for several reasons. Written laws provide a shared reference. This means the oral transmission of culture is disrupted, these laws can mutate or be lost. Written law also allowed a society to grow beyond a certain size.

SO if someone breaks a rule you can show evidence against that by stating the rule that was written down

Explanation:

Also, if it is not written down, people will most likely forget about the law