Another important aspect is the cost-effectiveness of sea freight shipping. If you transport cargo over long distances, sea shipping is the most efficient way. This has to do with large capacity of shipping vessels (the larger the capacity, the cheaper the price of delivery is)
But it should be noted that large capacity of sea vessels could lead to delays of delivery, in case of small quantity of cargo - because the vessel sails only when it is full and down. Another factor that provides low shipping costs is the fuel savings, because a ship requires less fuel than cars and especially airplanes.