Im really not understanding this paragraph in perldoc -f open

[grocery_stocker]

"In the three-or-more argument form of pipe opens, if LIST is
specified (extra arguments after the command
name) then LIST becomes arguments to the command
invoked if the platform supports it. The meaning of
"open" with more than three arguments for non-pipe
modes is not yet specified. Experimental "layers" may
give extra LIST arguments meaning.
"

I think what I'm drawing a blank on is why the list form wouldn't work
on platforms that don't support true fork.