IP forwarding Virtual server

You should consider checking out this article at AskF5: K7595: Overview of IP forwarding virtual servers

IP Forwarding Virtual Servers act more like routers than a typical virtual server. They forward requests to the destination specified in the request, as opposed to sending the traffic to a pool member.

One example is if you have a group of servers behind the BIG-IP, then you may use a IP forwarder to provide access to those systems for say, management purposes, with the BIG-IP acting as their gateway.