Milk stored in the freezer can be divided into chunks and water when thawed. It can be safely consumed, but it is not the wisest choice to add to your breakfast, for example to your cereal or coffee. No one would want to drink it!
The same happens to other dairy products too. For example, the tasty sour cream, should not be kept in the freezer for any reason. It becomes inedible once frozen, since they separate and curdle upon defrosting, changing the texture and consistency entirely.