General use cases

non-transparent
Standard ATS base case, either reverse proxy or explicit forward proxy.
full transparency
Common "transparent proxy" operation. The proxy is transparent to both clients and server.
inbound transparency
Useful for proxying without having to configure clients while enabling client addresses to be hidden from external servers.
outbound transparent
For a server farm provides a single address for external clients while the servers "see" the client without having to modify HTTP headers.