You select a route, then press the "Route Preview" button. Map view will then zoom to your current location and travel down the selected route as if you were driving. The map pans down the route so that you can see all the things you will be dealing with along the way without having to scroll around the map with your finger. Adding a "preview speed (1x, 2x, 3x, etc)" and a "pause preview" option would be a great addition to this.