Surveyors have been using GPS to do extremely precise surveys for years, fixing points with relative accuracy on the order of millimeters. However, in many surveying applications the job isn't just locating a point according to latitude and longitude, but rather fixing the positions of a group of points in relation to each other.
These points are often eventually tied into a control point that locates them with respect to the rest of the world, but the important relationship is really among the points themselves.
This distinction is important when it comes to accuracy. Relative positions are easier to measure accurately; this accuracy is achieved by using GPS in a very specialized way.