Math and art go hand in hand more than we ever think it does (such as, in perspective and drawing to scale). However, I never thought of approaching shadows in this manner. But, after viewing this incredible video that makes it easy, it makes total sense! If the shadows in your art are not consistent to each other in regards to the light source, it makes for an image that not only doesn't make sense (and the viewer won't know why), but awkward. But, HOW we approach this in order to be consistent, I suspect, is not all that organized. Watch this video (it's really short) and see how simple it is. You will love the mathematical approach even if you don't like math at all!