There is one other case where disk encryption on a server could be useful, though it is not widely applicable: if you have a need to be able to rapidly destroy data, say in the event of a physical security breach. Having data stored on encrypted storage devices can mean that to render the data on the drives unrecoverable only requires wiping the header region of the encrypted block device. That, in turn, means wiping at most a few KB instead of several GB, and thus the difference between many passes in mere seconds and hours for a single pass.
Having said that, this is probably primarily of significance to military, intelligence, and criminal organizations. Few others are likely to be faced with the need to destroy large volumes of data on very short notice.
(If you care about why, this is because most/all disk encryption systems use a randomly-generated master key to encrypt the data on the disk. A copy of that master key is then stored in a header, encrypted with the password or passwords known by the user. No plaintext copy of the master key exists, so to access the data you have to provide the user-known password and use it to decrypt the master key. Changing the password can then be done simply by re-encrypting the master password, rather than by re-encrypting the entire drive. If the encrypted copy of the master key is destroyed, then it doesn't matter how many people you torture to get the password, it's still useless for decrypting the data on the disk.)