Benefits of Mapped Face Meshing?
 

I don't fully understand what exactly it does. I mean,it definitely adds structure and unformity to the face, but looking at mesh statistics it doesn't do anything to the skewness/quality. What exactly does mapped face meshing do?

Mapped face meshing maps a structured mesh to the face. That is pretty obvious.

But I think your question is more why would you do this? Mapped face meshing is useful when the face is approximately rectangular, so a simple structured mesh will cover it with a very ordered and high quality mesh. The mesh it produces in this case is usually better than can be produced by other techniques. But if the face is not approximately rectangular it can produce some terrible meshes. So it is a meshing option which helps for some cases but not all - hence it is an option available if the user chooses it.

But why dont any of the metrics change before and after the mapped face mesh (skewness, element quality, etc)?

The really annoying thing about ansys meshing is that you can put things like mapped face meshing into the meshing tree, but if it does not like it then it ignores it and proceeds without a mapped face mesh.

So are you sure it actually generated a mapped face mesh?