Control points are used in Boundary Surfaces as an advanced way of controlling tangency lines across the surface. As an example, we will construct these two datum curves to be used to create a boundary surface.

 

Control points are used in Boundary Surfaces as an advanced way of controlling tangency lines across the surface. As an example, we will construct these two datum curves to be used to create a boundary surface.
Simply picking the two curves and no other constraints will give you this surface.
You can see that for each of the entity endpoints on the curves (A,B, & C), there will be a corresponding tangency line across the surface. This happens because Pro/E assumes a linear mapping of points from one curve to the next. So, a point 1/10 of the way down curve A will be mapped to a point 1/10 of the way down curve B. But we can adjust this linear interpolation with Control Points. Let's say we want to map Point A onto Point B. Going into the Control Points option in the Boundaries Surface Dialog Box, Pro/E highlights the endpoints on the first curve.
We'll pick the center red tick, corresponding to point A in the previous picture. Pro/E will then highlight the points on the other curve. Here we'll pick the second point from the left, corresponding to B above.
Choosing done and then OK to close out the feature, our new surface looks like this. You can see here that the surface now maps point A onto point B like we wished. There is still a tangent line at point C. This is a simple example, but this can be done with more complex boundaries surfaces with multiple curves in both directions.