This is a very cool feature and a big test effort time saver.
In your test plan you have set up more then one configuration. Maybe you need to test in different browser types, or different operating systems, even different languages. You create one test case to test a feature/requirement and attach it to a test suite, setting suite state to In Progress. When you go to the tab Test and open Run Tests there is an instance of your one test case for every configuration assigned to the Test Plan.
For very large applications or web sites that require testing in many different configurations this feature not only saves time in the creation of many test cases but it creates a marker that the testing has been done.
Feature Highlight:
Many Test Configurations – One Test Case – Instance of Test Case for every Test Configuration.