In the Barony of Bortofield, they grow sunflowers for the oil, and daisies for decoration. Because of this, they see flowers as a central circle surrounded by straight petals. So every piece of jewelry or embroidery that represents flowers in Bortofield, looks like this. No roses, no tulips, just sunflowers and daisies.
So why do you care? Because every piece of jewelry representing a flower in Bortofield looks like a daisy. Your players like jewelry, right? They loot it and sell it. Maybe you don’t care what jewelry they find and simply say, “jewelry worth 1,000 coins”.
Let’s come at it from a different tactic: In Garnock, pick pockets are so common that people don’t have pockets. Instead, they have a coin purse that they wear inside the front of their shirts on a chain around their necks. In Scaret, they have a fur pouch that they wear from their belt in front of the ... well ... in the front (like a sporran). In Brinston, they wear vests and great coats, both with pockets. If one of your player characters is a pick pocket, knowing how the people wear their money is going to be important.
Let’s keep going: In Helatia, the stone buildings are plastered in a white plaster in order to make them look bright and smooth. It also makes it nearly impossible to climb them. In Scaret, nearly all the cloaks are made of wool. Drying wool can be quite difficult, and many inns and even homes have a “closet” that runs behind the fireplace where the cloaks can be hung in a warm, dry place to help the wool dry for the next outing. So the coat closet isn’t next to the front door, but instead across the room. In Myork, they have recently switched the fashion of dress from wearing similar colors (green, emerald, grass, etc.) to wearing the exact color. Exact colors are actually pretty difficult to do - consistent coloration in fantasy era dyes and all. This makes outfits more expensive than they would be in other cultures.
Does this stuff matter? Yes, both in the role-playing aspects of the game and even in the actual game impacts themselves. Too often the GM needs to know some of these things, but because their worlds are not yet fully developed, they don’t know them. Getting back to the treasure and loot scenarios - do you even know which stones come from which parts of your world? Poor emeralds are found in the Slyvanian Forest, but they value the darkest emeralds, so they ship in the better emeralds from outside their forests. That matters. It helps a GM plan out the loot on caravans. It can even help plan out missions.