What does yawning do for the body exactly?

Big boost of oxygen.

I found this seems I could be wrong.

Im pretty sure it is the body releasing excess carbon dioxide

Yawning is exactly what you suspect—the body’s natural effort to wake up. It means you want to pay more attention and become more alert. It does not indicate that you want to go to sleep.

So keep on yawning and stretching because that’s how you get yourself to wake up. Those of us with desk jobs spend far too much time sitting. Yawning kind of saves our lives.

@JLeslie Funny I just read the link you posted and started yawning! The most contagious thing in the world if you ask me. I only wish kindness where as contagious as yawning.

Yawning is good for telling other people you’re boring them. Personally yawning makes me more tired and then I can’t stop doing it once I start. I think it’s a good thing to do as soon as you wake up.

yeah get a lot of oxygen, put out a lot of carbon dioxide

http://www.scientificamerican.com/article.cfm?id=why-do-we-yawn-when-we-ar