Officiall docs says about this command: "Move from one account in your wallet to another" link
Also from official docs: "Moves are not broadcast to the network, and never incur transaction fees; they just adjust account balances in the wallet." link
As I understand - account is a list of private-public keys (and assosiated metadata) So only action that we can do - move one or more key pairs from one account to another. But in this case we have a problem - we could not move any arbitrary amount of BTC, but only the amount that already associated with addresses. Strange command...
So what does this command actually?