Use the apiVersion flag for something
apiVersion is included in JSON templates. It's a great idea, which would allow the Azure servers to maintain backwards compatibility with the various API's to avoid situations where the API changes and breaks clients relying on older behavior.
Except that the Azure API does not seem to actually maintain any kinds of backward compatibility based on the apiVersion flag (or any other flag). The most enthusiastic Azure devs I know state that their scripts break now, "About once a month" based on API changes--which for them is a compliment! It used to be several times a week. This is not out of line with my own experiences with Azure starting in the summer of 2015.