You have N number of encryption keys for different parts of your data, then a single client server can only decrypt a small part of the data.
Since you need to request the key each time to decrypt things like key rotation become easier since you can do them centrally. Even if you can decrypt data X on a client node the key you got an hour ago for X doesn't work anymore, you must request a new one.
Then the server can do things like impose rate-limits. Maybe you can decrypt A-F, but only at a certain imposed rate, and alarms will be raised if the rate is exceeded.
Since you need to request the key each time to decrypt things like key rotation become easier since you can do them centrally. Even if you can decrypt data X on a client node the key you got an hour ago for X doesn't work anymore, you must request a new one.
Then the server can do things like impose rate-limits. Maybe you can decrypt A-F, but only at a certain imposed rate, and alarms will be raised if the rate is exceeded.