The explanation I heard many many years ago still seems right: yawning gets you more oxygen.
And if you need to test that, next time you feel the urge (meeting?), just breath deeply and it will go away.
"He and colleagues Michael Miller and Anne Clark analyzed yawning in parakeets as representative vertebrates because the birds have relatively large brains, live wild in Australia, which is subject to frequent temperature swings, and, most importantly, do not engage in contagious yawning, as humans and some other animals do."