maniacquilter explained it pretty well...you do not want bias edges around the outside of your quilt- bias edges stretch easily which can cause a lot of trouble when adding borders or binding. corner triangles are cut once diagonally- the straight *short* edges are the non-bias edges- they are around the outside of the corners- the bias *long* edge is inside the quilt. the setting triangles are cut in an X so that the outside edges are again on the straight grain- the bias edges toward the center of the quilt. if you choose to try to use your triangles that were cut incorrectly you should either really starch them well or add a lightweight fusible interfacing/stabilizer to keep the stretchy bias edge from creating a 'wonky' quilt edge. it can be done- but bias edges take much tender care.