Explain when the congruent complements theorem would be appropriate to use in a proof

The congruent complements theorem states that “If two angles are complementary to the same angle or to congruent angles, then they are congruent to each other”.

For example, if angleA and angleB are complementary and angleB and angleC are complementary. Since angleA and angleC are both complementary to the same angle, then they are congruent to each other.