When I am working on a face I am constantly checking the profile to make sure it is looking right. I find myself looking more closely at peoples faces and noticing what happens when they change expressions. For example when a person smiles their top lip will often flatten and that changes the profile quite a bit.
As I said in my previous post the felt needs to be very firm in order to get a well defined face.
A needle felt artist that I am very inspired by is Stephanie Metz Take a look at her figurative studies to see some wonderful 3D needle felting sculpture.