Volume encryption only protects against stolen disks, which is... highly unlikely. (The only scenarios I can think of are USB drives which get lost in transit -- think "station wagon full of tapes hurtling down the highway -- and law enforcement seizing the computers.)
Encryption at rest also protects from warrantee service where you’re sending a failed drive back to a vendor. I could see the drive being refurbished and send out with readable data on it if not encrypted.