When your polygons are convex and non-planar 'simple' quickly becomes an euphemism. You may even want to consider adjacent topology for something as 'simple' a

When your polygons are convex and non-planar 'simple' quickly becomes an euphemism. You may even want to consider adjacent topology for something as 'simple' as which of two possible solutions to take, when splitting a non-planar quad into two triangles. Triangulation is simple only when your polygons are planar and convex and aspect ratios of resulting triangles do not matter under any 2ndary circumstances. Some uses e.g. require avoiding thin, splinter-like triangles.