Since Vietnam is on ICT time, which is 12 hours ahead of New York, it is especially advantageous when it comes to daily quality assurance. For the past few years the flow has been pretty well honed:
Note how the US dev and VN QA work in relay manner with almost no overlapping time, resulting in a very productive development cycle. Had the QA been based in the US as well, the dev would have to wait until the next day or more for the QA to finish her work.
With a QA night squad, our US client now has a secret weapon, enabling him to deploy high quality code at half the speed of his competitors. At a fraction of the cost!