The big idea that excites me is that it does away with the concept of having uncommitted changes. Instead, every time you save a file in a repository it is automatically committed. It is the logical endpoint of the git workflow where you make lots and lots of little wip commits and then rewrite them into a sensible set of commits later, and the whole UI is designed around making that work well rather than being something that works but constantly feels like it's off the intended path.