Each LED corresponds to one unit test; if it passes it shows green, if it fails to run it shows red, if it fails to compile it flashes red.
It also runs speed and memory use tests and shows them in equalizer-type graph info. It bleeps and bloops.
So you can just sit there and jam away and write code and keep checking it in, and you get instant visual feedback if you break a unit test, or slow something down.
Ooh, it would be cool if there were various display widgets and various outputs, and you could actually run physical wires to hook them up. Like oldschool telephone switchboards. So maybe I only have like 4 speed display graph panels, but I have 20 tests that can output speed information. I can reach over and plug the wire from the test I want to the panel I want to see it on.