The features that are generated using the detect features step of scenProc are not simplified. Before these polygons would be a bit blocky because of the raster image that has been converted into the polygon. But with the simplification a more smooth polygon results. In the image below you can see an example without (left) and with (right) the simplification applied.
The simplification makes the polygons less complex and therefore also reduces the size of the AGN files. And with this simplification it also becomes possible to use the feature detect polygons for buildings. For the blocky polygons it was not possible to calculate the best fitting rectangle correctly, but for the simplified ones that no longer applies.