Why is it important to have your cargo insured during the international transit? Mostly because of the limited liability of the shipping vendors.
Other parties involved (warehouses, freight forwarders, trucking companies, ports, etc) all carry limited liability and will never automatically cover the full value of the cargo they handle. This is why international shipping insurance is a very big business because it provides the required coverage in case something happens to your shipments during the transit.
There are 2 basic types of international shipping insurance you can get: ALL RISK and TOTAL LOSS. All Risk will cover any loss or damage occurred to your cargo during the ocean transport. It does have a deductible and possibly some exclusions but this is the most encompassing coverage you can get. Total Loss only covers the complete loss of cargo - it will not cover for minor damages. In other words your shipment must be completely lost, stolen, ruined, etc for the this coverage to apply.