Why move the Work Plane onto a curve

One possible reason for moving the Work Plane onto a curve would be to create a spined solid connecting some section curves. The orientation needs to be the same for all those curves. Otherwise, you might get some unexpected twistings.

In this illustration, the Work Plane has been moved onto each of the three curves, always using the same reference plane (the one in the picture).

The Work Plane is automatically set this way:
 

• The Z axis is the direction of the tangent to the curve in the selection point
• The X axis is the direction of the normal to the curve
• The Y axis is the direction of the binormal.

Another way to get the same result is to use the Spined Curve command.