case Foos of
  _ when IsBar -> baz;
  []           -> quux;
  [Foo]        -> Foo
end.

vs.

case {IsBar, Foos} of
  {true ,     _} -> baz;
  {false,    []} -> quux;
  {false, [Foo]} -> Foo
end.

vs.

case IsBar of
  true  -> baz
  false ->
    case Foos of
      []    -> quux;
      [Foo] -> Foo
    end
end.