Key Considerations:The majority of Instagram use is "mobile". Mobile phone screens are, of course, small, so in order to use all the screen real estate, its got to be 9x16. Facebook and Instagram both encourage the format.
Technique: Most video is shot 16X9 "landscape" rather than 9x16. So there are considerations to make during the shoot, AND the edit.
Results: It's all about campaigns and measurement.
Keys to Success: For someone from a film and video background, it is really almost cognitive dissonance to have an online platform dictate to provide video 9x16.