Using the shipping server on an exposed host enables anyone coming in from the network to fill storage bays on the local network, on any machine where a shipping server is available. To avoid full disks and the related problems:
In normal update packets, information is not encoded. Therefore, anyone shipping packets across an unsecured network must encrypt the packets. Also, the format of an update packet is not very complicated; a dedicated programmer could figure out the format and create a packet with operations that damage a schema repository or user database. Encrypting the data makes this kind of attack much more difficult.