Cargo (Inland Marine) policies are used to insure goods for loss or damage to the goods during shipment. All carriers of goods for hire, are bailees and have a duty towards the property entrusted to their care. The carrier is liable for the goods from the time it receives them until they are delivered to their final destination.
There are vast differences in the coverage of cargo policies issued by different companies. Be sure to check exclusions and limited coverages on your policy. Most cargo policies exclude "rust" when hauling steel and almost all policies require "tarps" when hauling on a flatbed trailer.