There are many reasons ways the REST API can be utilized, but why should we care? Why are any of these reasons so good we need to have the API in core vs. a plugin? I will take a non-code approach to explaining from the basics, why the REST API is not just a good thing to have for development, but a good thing to have for WordPress to keep it going and keeping it relevant. Then you can be the judge if it is a good and necessary addition.
Prerequisites
Knowledge that the API exists, and desire to learn about it. This will be a good intermediate / low-level talk for the reasoning behind the API and why it is good.