A sequence of transformation can move two congruent figures to the same place (vertical / horizontal shifts). This causes them to perfectly overlap, proving their congruency.
A sequence of transformations can be used to show that something is similar, because if one were to transform a figure with only shrinks / stretches, one can shrink / stretch them to make them congruent. If only shrinks or stretches were done, and if the result of the transformation is congruent to the other figure, then the figures are similar (sides are proportional and shrinking/stretching them proves proportionality to other figure).
