This dialog lets you create a closed point curve when you click to create a point in the same location as the curve's first point.
Create panel > (Shapes) > Point Curve button > In viewports, draw a point curve and click to create a point in the same location as the first point in the curve.
Modify panel > Select a NURBS object. > NURBS toolbox > (Create Point Curve) > In viewports, draw a point curve sub-object and click to create a point in the same location as the first point in the curve.
Interface
Yes
Closes the curve and ends curve creation.
No
Keeps the curve open and does not end curve creation.