Explanation/Reference:
At any time when you are planning what to test, you can add test configurations and set them as the default configurations for your test plan. When you next add test cases to the test plan, a pairing of each default configuration with the test case is added to the test plan. When you run the tests from the test plan, these pairings called test points are shown and each can be run individually. Test results are saved for each test point.
You can also override the default test configurations for the plan and set different default configurations for a specific test suite. When test cases are added to these test suites, a pairing of each default configuration for the test suite with the test case is added to the test plan as shown in the following illustration.

Reference: How to: Select Different Test Configurations For a Test Plan or a Test Suite