It may not seem like a big deal, but changing the routing of your driving directions can be a very good thing.  Googles computers don’t know everything about every road.  They may not know that 20 miles of I82 are being ripped up an re-paved, and that you want to avoid I82 at all costs.  So when Google Maps has you zipping along I82, what do you do?  Simply click and drag your route away from I82, and Google will update your turn-by-turn directions to direct you around the troublesome I82.

Here’s the link to the Google page about the new feature
http://maps.google.com/help/maps/directions/index.html#utm_campaign=en&utm
_source=en-mapshpp-na-us-google&utm_medium=mapshpp