Routing helps you in dividing your application into logical views and bind different views to Controllers.
What is AngularUI Router?
The UI-Router is a routing framework for AngularJS built by the AngularUI team. It provides a different approach than ngRoute in that it changes your application views based on state of the application and not just the route URL.
Below are some good examples of Angular UI-Router in action.
Introduction to ui-router by Egghead