Art is design.
One important component of design is the kind of edges you choose to render.
Here’s a pic from ConceptArt.org’s Paintovers for Posterity that’s been of great use to me
Paying attention to these kinds of edges doesn’t just help me render different textures…it helps me lead the eye around my work. Hard and firm edges tend to draw the eye towards them (and the clearer the edging/shape read, the friendlier an overall composition is; hence why children’s images and cartoons are so well lit), while lost edges add mystery and tension. Good times!