Why do trucks have to be weighed?

Truck have to be weigh because you have to know how strong or thick it is like if a truck is light, it means it's weak and if you put a heavy box that contain something that need to be transfer, then the box would break the truck for it weight. If the truck is too heavy, then when you drive the truck, it would either sink for it weight, it might become very slow, or even the engine wouldn't even work. This is why a truck have to be weigh.