"Waze is a social mobile application providing free turn-by-turn navigation based on the live conditions of the road.
100% powered by users, the more you drive, the better it gets. Join the community of drivers in your area today!"
Personally I leave it running each day on my way to and from work as it's fantastic at showing you where traffic congestion is building up based on the driving conditions other waze users' are finding themselves in. Also, as you get caught in a jam you automatically report back to all the other waze users that you're stuck in traffic. Great for those roads (Such as the Hagley road in Birmingham) that you're not sure are going to be busy.
If you use it as a GPS navigation system, it automatically modifies your route each time waze learns of traffic along your route.
Well worth using for the daily commute, Can't stress how pleased with the app I am.