All the mesh boundaries are highlighted in green.

The hole is filled with a mesh that attempts to maintain the curvature properties across all of the triangles that fill the hole (when Quality option is set to Faired).
Use Edit > Undo to undo any number of hole fillings.
A flowline is created between the two profiles.The profiles and flowline are view based, and will disappear if you change the view. If this happens, you can click Patch View to reset the view

A mesh patch is built between the green lines. Shading the mesh will help evaluate the result.