Here's a topo map and position marker example from a backpack trip to an area I'd never been to before. The red triangle is the Position Marker in the above screenshot. Notice no GPS coordinates are shown, they're internal to the GPS and totally unnecessary for this discussion. What matters is your position in the context of the topo map. I had been hiking for several hours and my destination was the Venable Lakes, roughly 5-miles and 3,000 feet higher than the trailhead. How close was I and how long before I reached my goal? No guessing required, the Position Marker on the map made it easy to know both distance and ETA.

This screenshot, again shows my absolute position via the Position Marker, red triangle. In context is my tent location, both lakes and Venable Pass. It is this position context which makes topo maps inside a GPS so useful. If the morning brought pea soup fog, I'd still know my way to my next destination without visual references.

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.