[moved] Difference between Perfect E and Finite conductivity of materials in HFSS

Can anyone explain about the difference b/w Perfect E and Finite conductivity in HFSS.
When should use those perfect e and finite conductivity options for materials?

Thanks in advance for your help...

PEC materials have bulk conductivity = 1e+30 [Siemens/m].

Where to use PEC
where to use Finite conductivity materials

If you don't care about field penetration into the conductor or resistive losses, it's better to use PEC for simplicity. HFSS treats the surfaces of PEC object as PEC boundaries so that there exist no electromagnetic field inside. You can define PEC boundary on 2D sheet objects to represent lossless conductors such as transmission line traces or patch antenna elements.