ITopologicalOperator.Intersect V.S. ITopologicalOperator6.IntersectEx?

Hi Everybody:

I am looking for a method to find the 3D intersection of two polylines with Z-coordinates.
I checked the functions ITopologicalOperator.Intersect and ITopologicalOperator6.IntersectEx. The difference is that IntersectEx has an additional boolean parameter bNonPlanar. What is this parameter for? Is it a switch to get the result in 3D?
Thank you!