Privacy, Security, and Debugging Considerations
Unfortunately, NAT reduces the number of options for providing security. With NAT, nothing that carries an IP address or information derived from an IP address (such as the TCP-header checksum) can be encrypted. While most application-level encryption should be ok, this prevents encryption of the TCP header.
On the other hand, NAT itself can be seen as providing a kind of privacy mechanism. This comes from the fact that machines on the backbone cannot monitor which hosts are sending and receiving traffic (assuming of course that the application data is encrypted).