SNAT Pool allows using more than 1 IP address for SNAT purpose. Since SNAT is Port-Address-Translation, ephemeral ports on single IP will run out (despite having some 65000 ports, it can run out much faster with certain App/protocols) with increased amount traffic, so SNAT pool allows virtually limitless scalability.
By assigning SNAT pool or Automap to individual virtual server, you can be selective about which virtual server gets SNAT applied, vs. all. However, if you want to do this for select source IP/client, then you may need to use iRule attached to the virtual server.
Nimbostratus
