it's not about accuracy, it's about flexibility. Rather than following the GPS which may take you over 2 lane windy mountain roads, you can stay on major highways by using an Atlas or take shortcuts that others have recommended. I also use online mapping like Google Maps and Mapquest. Online maps and GPS's have 2 options - shortest or fastest routes. Sometimes you need a combination of both. Also RV settings on GPS's use truck routing which takes you out of the way sometimes resulting in more mileage.