Google Maps Navigation is a very useful extension of Google's existing mapping services, which provides many features expected of traditional GPS navigation: voice guidance, automatic re-routing, destination searching and more. Since it is integrated with other Google services, it can also overlay things like geographical information, Wikipedia articles and a lot of other metadata.
One of the most attractive aspects of Google Maps Navigation on an Android is the fact it is added on to existing hardware. GPS navigation devices can be very pricey, particularly for ones that are feature-rich. Even the entry-level car navigation units are not easy to swallow. With Google Maps Navigation, you are turning an existing device into a GPS navigator for no cost. What it may lack in features it will make up for in being free, though Google has clearly attempted to offer as much as possible.
If you own an older Android device, now is your chance to download the navigation software and give it a try.