Yes, more or less, but if you extract a triangle three new vertices, three edges and two faces pointing in opposite directions are generated; that means that all the newly generated edges will become hard, whereas we might need only one or two of them to be hard.
The way I see this feature (which is the way it is implemented in Blender btw), edges are considered rather than faces: if an edge is marked as hard, or if it connects two faces whose normals describe an angle wider than a threshold previously set by the user, then in its place two edges are generated (one for each face); if not, the old edge is retained.
I hope I made myself clearer this time
The way I see this feature (which is the way it is implemented in Blender btw), edges are considered rather than faces: if an edge is marked as hard, or if it connects two faces whose normals describe an angle wider than a threshold previously set by the user, then in its place two edges are generated (one for each face); if not, the old edge is retained.
I hope I made myself clearer this time