I find the traffic alert system in the Nav system to be pretty helpful. I usually program my destination, even though I know how to get there, so I can see if there are any traffic issues on the planned route. It alerts are typically quite accurate. If you click on the alert icon it will give you all the alerts in the area. There can be delays in update, such as where there was congestion that has subsequently cleared up...
Also, I use a split screen where the left is the normal Nav, and the right enabled to map. You can then keep the right hand map scaled higher which will point out traffic alerts in yellow farther away. It gives you better visibility on the gray map vs. the color route map on a shorter scale.
However, it does not replace Google Maps and its traffic layer which is much more detailed.
I don't know how different the data is in various geographic areas, however.