YouTube recently started recommending Chinese cooking videos. This particular cook has a curious habit of rubbing cornstarch all over the chicken breasts before washing them off. Is there an advantage to cleaning chicken with cornstarch? Or perhaps an alternate explanation? Some people have suggested it's for tenderizing or velveting but those aren't particularly satisfying answers.
The closed captioning on the video stated that the chicken in the recipe has to be 'kneaded' for two minutes. This does suggest that this step is meant to tenderize the chicken. Cornstarch in principle does nothing to aid that process. However, cornstarch is excellent at absorbing liquid, which leads me to believe it's there to catch any liquids coming out of the chicken due to the tenderizing.
This is little more than a hunch, though, and does not really explain why the chicken could not be washed after tenderizing without using cornstarch.