Our nasal passages were designed to freely move air in and out of them.  Chronic nasal congestion has been known to alter the structure of the palate and jaw. It may also be accompanied by nasal congestion, which leads to mouth breathing. 

Mouth breathing leads to disruptive sleep, and when sleep is impacted, a whole host of symptoms can snowball from there: fatigue, trouble focusing, irritability, behavior challenges, mood swings, anxiety, and, if it persists for many months, the immune system itself.