Many crafts require the edges of materials to be protected. Usually with good reason. The dressmaker, upholsterer, sailmaker, are concerned that raw edges will fray and material will unravel. They have a variety of hems and seams to choose from. The joiner and cabinet maker cannot wrap their materials around as can the seamstress. The end grain of wood is prone to splitting, and wherever possible is protected. Builders protect the end of their scaffolding planks with steel strips (which in turn are protected by galvanising). The surface of many bookbinding materials is less absorbent than the edges, which readily absorb unwanted moisture into the fibres. That is useful when gluing, less helpful when books are stored in a moist atmosphere.
I believe that this tradition of "hiding the edges" through necessity, has led to equating it with "good workmanship". This, in turn, leads to thoughts that "showing an edge" is a result of bad workmanship. There is sometimes truth in this, but please do not apply such thoughts with too much enthusiasm. craftsmen have to bow to the necessity of economy of materials and effort which play an important part in the everyday modern life of their customers.
Here is a link to notes on making butt joints - which hide some raw edges [112533].