Airfreight companies use dimensional (dim) weight to cost out shipments primarily because of the density of the product. Dimensional weight takes into account the space a package occupies in relation to its actual weight. This is particularly important because lighter, bulkier items can take up more space in an aircraft than their weight justifies, affecting the overall capacity. By considering the density, airfreight companies can charge more accurately for transportation, ensuring that both heavy and light, bulky items are accounted for fairly.