Answer:
If, for example, you have a grid with different grid spacing in some areas, you cannot use the load generator with only one defined area load plane. The load would otherwise be determined according to the size of the area load plane and applied to all members (except the boundary members) with the same load value (see the image on top).
However, if the area load is divided into several sections (dialog box section "Boundary of the Area Load Plane"), the load is distributed correctly. This is shown in the bottom of the image.
