HI Stanislas,
Thanks for you response.
So to recap, correct me if I'm wrong:
There are 2 options in using server & virtual server in GTM:
1. Server is LTM (uses mgt IP), virtual servers are LTM virtuals (virtuals IP/port).
2. Server is standalone, virtual server is same server (same IP) + service port.
But that still doesn't explain the needs for physical server. I could create one dummy physical server, and declare all of my virtual servers in resource + service ports (no matter what they are, LTM virtuals or single dedicate servers). Anyway load balancing is done in wideIP logic and in pool you can group any virtual servers you want. So don't see physical server play any role in load balancing job.
Hope I make myself clear here.