AFAIK, ssh is always an option with rsync; obviously its a CPU overhead computing the encrypted version and decrypting at the other end.
Whether you need it as a security measure is a (your) judgement call.

As I said above, for a local cp (inside one machine) its pointless. OTOH, if you are going over any network, even a LAN (eg NFS), you may be worried about interception; depends on the data really.