This is a screenshot taken with a digital camera, pardon the quality. The key point here is the black triangle in the center of the image, that's the GPS Position Marker. It shows your absolute position on planet earth and centers the map around the PM. As you move, the OS within the GPS constantly refreshes the map such that the PM is always in the center of the map.

If you look to the right, you'll see a dotted blue on white tracklog, that's the path I took to arrive at this 13,000 foot summit. At any point on that track, had I looked at the screen, the PM would have shown my true position and the map would have been centered around the Position Marker.  From the point of off road, off trail navigation, the PM centered on a high resolution map beats any combination of paper map and compass. You always know where you're at, not simply as a Latitude and Longitude, but as a point on the map. The map gives context to your position and moves navigation to the 21st Century.

This is the larger Mapsource view of of the same hike. The emphasis here is the tracklog, yellow being to the summit and green coming back, somehow I managed to turn off the GPS on my return and no tracklog until I noticed it was off. Opening the tracklog in Mapsource shows a spreadsheet of time and position.