There are several reasons why this position is limited in duration. First of all, it is more tiring for the baby to be turned towards the world. In this position, the baby is very stimulated because he is exposed to the unknown and to all kinds of images, situations and faces. This can be stressful and he has no opportunity to comfort himself against you. Also, his head is not as well supported in this position as in other positions and it will take more effort to hold it. He'll get tired faster. If he moves around a lot and tends to stand up, you may have to move his legs back to a nice sitting position with his knees up. Be sure to check the circulation in the legs and don't over-stimulate the baby. It is also important to note that the facing position is heavier for the carrier and puts more load on your shoulders and back.