Why is it important that the term “locked” is used when making the following statement? You can use a locked compass setting and a straightedge to draw two congruent segments.

You use a compass to draw an arc (or a full circle). The radius must be kept the same so that you can copy the length of the segment properly. If the compass could move freely, then it is unlikely the arc will be a piece of a circle, and rather some squiggly curve. So this is why the compass width must be locked into place.