Google continues to push its Maps product on iOS in the latest update, version 2.6. The app now alerts the driver when faster routes become available when navigating. This reflects functionality found in dedicated sat navs. Rather than simply offering several routing options at the beginning of your journey, Google will keep aware of traffic and road conditions in case a faster route appears later.
Theoretically, this means you are always on the fastest route possible when navigating. As always, the app is free.