>>526590>AFAIK anything 3D is done in tris. Quads are just a representation of the underlying tri mesh that is easier to work with
You "know" wrong.
Transformations are performed using vertices, not faces.
IOW, If you define a quad, than the transformation creates a surface between 4 points. The problem with n-gons greater than 3 is that the surfaces are rarely planar, while tris are always planar.
Nonplanar rendering can result in some aesthetically displeasing surface distortions. In these cases, you can triangulate the offending n-gons are add more - it depends on the artist's taste.