Materials influence how artists make their work and how viewers perceive it.
I.E- Say you were painting a bear, and you want it to look realistic. Understanding the way fur/hair looks plays a big part because you want to paint it exactly how it is in real life. You don't want the texture to look rough like a carpet, you want it to look like fur. So understanding how the fur looks helps you get an idea of how to paint it convincingly.