/ic/ - Artwork/Critique

Is painting via opacity/tranparency/erasure a legit technique? By that I mean I start off with a flat highlight layer. I then mask it with a shadow layer on top. The process involves erasing parts of the shadow layer where I think light hits, which then reveals the light layer underneath it. Darker values are obtained not by colorpicking a darker value, but via opacity (repeated brush strokes over one area until desired value is obtained.) It takes a long time, but it's more intuitive for me than the usual block-in method, and it feels like I can control the edges better. The main 'brush' here are hard and soft erasers. The only limitations I see are low contrast references.