In reply to Peter Knight.

Totally agree. WordPress has so many APIs for similar things. Wherever a form and fields, there is an API: meta box, comments, widgets, shortcodes, terms, settings pages and even customizer. Each of them was implemented with different purposes and thus, APIs. Not only the API, the way WordPress handles the data is different, too. It's not only add extra works to developers, but also waste a lot of time for users to just learn to use.

I hope Fields API can resolve this problem by providing an abstract layer between what really happens with the data and what users see.