I also love using the eraser to create depth and 3 dimensionality.
Every drawing is an experiment.
You never actually know how you are going to achieve the look you need until you get to each moment of making marks.
For me each drawing is a lot about learning to make the overall mark and then using the eraser to create the atmosphere for that section of the portrait. Actually drawing with the eraser. This is all very much guided by intuition which is a fabulous cross over between the physical nature of creating the drawing and the spiritual nature of deep connection to my inner wisdom and divinity and then trusting in what I am being told and that it will all turn out.
I am also loving the deep delving with only pencil (instead of the laborious laying down of 30 or 40 or more layers of paint - I paint by glazing), limiting myself to only a few grades of graphite pencil or two pastel colours. The monochromatic finish to me has a more soothing and deeper connection as the brain does not need to interpret any colours- it's as though all the extraneous detail is being removed so that all you see is the character of the portrait without any distraction.
I find I need to work progressively around the drawing to balance out the tonal values of the overall work as well as the section I am working on simultaneously. Eg if the hair is the deepest tone I will create that first to set the scene for the face tonal values. As I move around the drawing the tonal values are constantly being evaluated and updated as needed. Sections being reviewed and touched up against new sections that are created.
Each drawing is a work of intense detail and patience one tiny mark at a time.