Complex sentence: A "digon" is considered degenerate face of a polyhedron because it has no geometric area and overlapping edges, but it can sometimes have a useful topological existence in transforming polyhedra.
Split into simpler sentences: A "digon" is considered a degenerate face of a polyhedron because it has no geometric area and edges are overlapping. But sometimes it can have a useful topological existence in transforming polyhedra.