Michael,

Here are a couple examples:
Corel.jpg and Corel000.jpg are from MoI which show basic editing of control points for a polyline.

I created the same polyline in Corel Draw as Corel002.jpg. It has the same type control points.

If I select one point and "Convert to Curve" I get Corel004.jpg. You can see that pont and teh previous point in the segment now have "flyout control arms" (there is probably a technical term for those but the name escapes me) that adjust the spline curvature without moving the contol node point.

Corel005.jpg converts the second segmet to a curve. Now control point two has two "flyout control arms" that can be "tangent" (for smooth curve) as in Corel005 or "independent" for sharp corner as in Corel006.jpg. These arms and points can be moved independently, added, removed or converted back to plain control points. Some type of function such as this would be very useful I think.