Windows in a building may seem purely for aesthetics, but they have functional purposes as well. Not only do they allow natural sunlight inside to provide sufficient illumination to the room, but they also keep other elements such as dust, wind, critters, and pests from entering inside.Windows in a building may seem purely for aesthetics, but they have functional purposes as well. Not only do they allow natural sunlight inside to provide sufficient illumination to the room, but they also keep other elements such as dust, wind, critters, and pests from entering inside.