What are the advantages and disadvantages of Vessel Sharing Agreements (VSA) between shipping lines?

The mode of cargo&container transportation more appropriate to present economic circumstances and become standard practice for shipping lines, shipping companies are getting together to share the space on their ships to allow for higher capacity, .. . As a result, many shippers are finding out that their containers are not going on the ships they thought they would. The good part is that their rates, contacts and contracts do not change with these agreements.VSA's are preferable for the shipping industry. Since they are between the carriers outside of their customer's, the agreements allow for the shipping lines to keep freight costs lower since they do not need to account for empty spaces on their ships. These agreements are also better for the environment since there are less unnecessary ships giving off pollutants into the air. For shippers, these agreements should not affect much except that they may be paying a different rate for the same commodity on the same vessel as one of their competitors.