The use of thirds in design is a technique that allows for a harmonious and balanced arrangement of elements within a composition. By dividing the design into a grid of nine identical boxes, created by two horizontal and two vertical lines at equal distances, the rule of thirds guides the placement of key elements. This technique helps create a visually pleasing composition by placing important elements along the grid lines or at the intersecting points, allowing for a more dynamic and engaging design. By utilizing the rule of thirds, designers can easily create a sense of balance, visual interest, and flow in their designs, enhancing the overall aesthetics of the composition.