I use the built in GPS, and I use it even for my daily commute. The biggest factors for me are that it uses google maps, it is traffic aware, and the screen is large enough to show detailed traffic for the route.

The UI just got a refresh with version 8.0 and it is now even easier to use. With a single swipe I can navigate to home or work (it is location and time aware, so it will navigate me to the right destination automatically), and the navigation now sticks to the top half of the screen when I have two apps open. I tend to leave the nav in fullscreen mode though since I like to see more of my route.

Its critical for long distance trips because it will also navigate you through superchargers automatically as needed, and will tell you how long you will need to charge at each, along with an estimate of your trip time. I have taken a lot of long trips since getting the Tesla so this has been invaluable.

Supposedly the next update will use the navigation to guide the autopilot (it will take exit ramps between highways automatically).