Because CGAL does many magic geometry operations for me that (having tried to code myself) are a PITA to implement.
But every now and then you end up with a link error like this:
"CCBToPolygon(CGAL::I_Filtered_const_iterator > > > >, GIS_vertex_data>, CGAL::Arr_extended_halfedge > > > >, GIS_halfedge_data>, CGAL::Arr_extended_face >, std::allocator > > > >, GIS_vertex_data>, CGAL::Arr_extended_halfedge > > > >, GIS_halfedge_data>, CGAL::Arr_extended_face > > >, CGAL::Arrangement_2 > >, std::vector > > >, std::allocator > > > > >, CGAL::Arr_segment_traits_2 > > > >, CGAL::Arr_extended_dcel > >, std::vector > > >, std::allocator > > > > >, CGAL::Arr_segment_traits_2 > > > >, GIS_vertex_data, GIS_halfedge_data, GIS_face_data, CGAL::Arr_vertex_base > > > >, CGAL::Arr_halfedge_base > > > >, CGAL::Gps_face_base> >::_Is_valid_halfedge, CGAL::CGALi::In_place_list_iterator > > > >, GIS_vertex_data>, CGAL::Arr_extended_halfedge > > > >, GIS_halfedge_data>, CGAL::Arr_extended_face >, std::allocator > > > >, GIS_vertex_data>, CGAL::Arr_extended_halfedge > > > >, GIS_halfedge_data>, CGAL::Arr_extended_face > > >, CGAL::Arrangement_2 > >, std::vector > > >, std::allocator > > > > >, CGAL::Arr_segment_traits_2 > > > >, CGAL::Arr_extended_dcel > >, std::vector > > >, std::allocator > > > > >, CGAL::Arr_segment_traits_2 > > > >, GIS_vertex_data, GIS_halfedge_data, GIS_face_data, CGAL::Arr_vertex_base > > > >, CGAL::Arr_halfedge_base > > > >, CGAL::Gps_face_base> >::Halfedge, int, std::bidirectional_iterator_tag>, Polygon2&, std::vector >*, double (*)(CGAL::I_Filtered_iterator > > > >, GIS_vertex_data>, CGAL::Arr_extended_halfedge > > > >, GIS_halfedge_data>, CGAL::Arr_extended_face >, std::allocator > > > >, GIS_vertex_data>, CGAL::Arr_extended_halfedge > > > >, GIS_halfedge_data>, CGAL::Arr_extended_face > > >, CGAL::Arrangement_2 > >, std::vector > > >, std::allocator > > > > >, CGAL::Arr_segment_traits_2 > > > >, CGAL::Arr_extended_dcel > >, std::vector > > >, std::allocator > > > > >, CGAL::Arr_segment_traits_2 > > > >, GIS_vertex_data, GIS_halfedge_data, GIS_face_data, CGAL::Arr_vertex_base > > > >, CGAL::Arr_halfedge_base