Without the judicial branch, the executive branch would be able to do whatever it wanted, without fear of being challenged by the other two branches of government. The executive branch could, for example, make laws without the approval of the legislative branch, or it could refuse to enforce laws that it did not like.
Without the judicial branch, the legislative branch would be able to pass any laws that it wanted, regardless of whether or not they were constitutional. The legislative branch could, for example, pass a law that discriminated against a particular group of people, or it could pass a law that took away the rights of individuals.
The judicial branch is essential to a functioning democracy. It ensures that the other two branches of government are held accountable for their actions, and it protects the rights of individuals.