If a web app and a database are on the same server, what is the security benefit of encrypting database data? Obviously passwords should be hashed either way.

I assume that if an attacker can inject some SQL or server code he would be able to view database data. Could somebody more precisely outline the security implications?

Edit: To clarify I was talking about encryption of data. The encryption method is not deterministic so enc(data1) != enc(data1)