It's quite useful for making delicate sauces as well as pastries and cakes for people who cannot tolerate wheat gluten (it's actually made from maize, not wheat flour).
Add an egg white to your stir-fry marinade and it will combine with the cornflour to create a protective layer which keeps the chicken juicier.
You can keep the soy, salt, sesame oil, rice wine etc in there too, it'll still work.