#Selenium: UI-Element helps to insulate testcases from change in underlying application

With traditional Selenium IDE recorded tests, small modifications to the presentational layer of a web application can break the ability of the test to locate elements on a page. Tests should be more resilient to change, such that testcase breakage can be minimized with careful test construction, and can be fixed at a central point as opposed to in all affected testcases. This calls for some mechanism of abstracting the locator.

source: http://goo.gl/zJ8d

Selenium UI-Element Reference