I use it to make dual gauge track. The mesh for the 3 rails can be a bridge type spline and 2 invisible track splines actually carry the ng and sg trains or the 3 rail mesh can be set as a normal track spline to carry just the sg and the ng carried on an invisible track spline layed along side it.
It's also required in making dual gauge turnouts and some of the finescale turnouts.
Quite useful stuff actually.
Bob Pearson