What is a difference between follow path and follow path and 1st guide curve when doing swept in SW?

When doing a swept with a guide line there is an option follow path and follow path and 1st guide line. What is the difference?

2 Answers

1STguide curve, when properly drawn, will allow controlled twisting and deflection along the path.
Perfect illustration here:
http://grabcad.com/questions/tutorial-creating-a-swep-using-a-path-and-a-guide-curve

What about follow path and follow path and 2nd guide curve?