Using this command, you can extrude any edge to a line segment going thru the architect which is also parallel to the edge. Perpendiculars are dropped from the corners of that newly form line segment to the original corners of the original edge.

In short; 3 line segments (orthogonal) will replace the original edge. In short, this creates a rectangular shape, with one edge of the rectangle missing (which is where the first edge used to be)

You can always locate the architect accurately using the headsup command line, before invoking this action.

This is different from stretching the edge. There is another command for stretching. See that here