The primary purpose is to carry goods from one place to another. It does so with much better speed and mobility. Cargo trucks are also ideal on a construction site. They can carry bricks, cement, people, dirt, and heavy machinery.
Moving livestock is also an observed use if the cargo bed walls are kept high. The open roof often keeps animals from panicking.
Trucks deliver such items as fertilizer, feed, and fuels; go into the fields as part of the harvest equipment; and haul the crops to markets, warehouses, or packing and processing plants.