What is the benefit of yawning?

Answer 1

A yawn (synonyms chasma, pandiculation, oscitation from the Latin verb oscitare, to open the mouth wide[1]) is a reflex of deep inhalation and exhalation associated with being tired, with a need to sleep, or from lack of stimulation. Pandiculation is the term for the act of stretching and yawning. Yawning is a powerful non-verbal message with several possible meanings, depending on the circumstances. It is also claimed to help increase the state of alertness of a person. It has been shown not to be from lack of oxygen, because it reduces oxygen intake compared to normal respiration. Another speculated reason for yawning is nervousness - paratroopers were once noted yawning right before their first jump.[citation needed] The exact causes of yawning are still undetermined.

for some of the hypothetical reasons and some medical reasons for yawning, read the article at the site below.