I have a question about design. I've just been through the code of the ToDo template of Visual Studio for building a SPA with BreezejS and AngularJS.

There is a todo.model.js file that do various initialization. One interesting thing is that it extends the TodoList Entity with some additional function (addToDo).

What is the advantage of doing so, over having the addToDo function in the todo.controller instead and adding it to the $scope ?