Its origin is the 3rd, 4th and 5th ribs close to costal cartilages that connect the ribs to the breast plate. The insertion point is the medial superior surface of the coracoid process of scapula. In short it connects your ribs to the top of your shoulder blade and it pulls it down and forward.
Assuming that you have a stable scapula that is in its correct anatomical position, when you contract the Pectoralis minor, it helps you lift the ribs.
What would happen if your pec minor is too strong or too tight? It pulls the insertion towards the origin that means it pulls the scapula up and over towards your breast plate and gives you a rounded shoulder look.
This pattern of moving the insertion point toward origin repeats in many muscular imbalances. When you are clear about this, you’ll recognize a poor posture, many of shoulder weakness and injuries as well as lack of strength in shoulder motions could be connected to the pull the pec minor exerts to move the insertion towards its origin.
You also recognize that one of the first steps in improving your posture, getting relief from shoulder pain and improving your shoulder strength is to reduce the tension within the pec minor.