Why white metal?
An advantage of white metal is the way it holds up under drilling, scoring, sanding, etc, as it is much more dense than styrene plastic and has a much higher melting point. Being quite malleable, it can be bent without fear of breaking and this is a useful characteristic when it comes to final alignment tweaking.
Another advantage of white metal over styrene plastic is strength. Metal parts will not warp under the weight of a built model regardless of the size of the aircraft, no matter how many years it stands on display.