I'm a big fan of private APIs, and all for keeping API access tailored to meaningful groups of users vs. just opening up data to the public, without first thinking critically about the possible pros and cons. With that said, I always encourage API providers to seriously consider the outside-in effect, when APIs are designed to be as accessible as possible, allowing unintended things to occur around your API resources.
It isn't just about the developers who are directly working with your API, it is also the entire API industry, and service providers that serve it. A number of companies exist across the API space, providing valuable products, services, and tooling that is derived from one or many API platforms. The API space is big enough now, it isn't just about the handful of strongest players, it is about the entire community.
An example of this is with API ChangeLog, a monitoring service for API documentation. The API ChangeLog keeps an eye on 68 of the leading APIs, and tracks on whether or not they have updated their API documentation, and keeps developers informed of the changes. These types of services benefit both API providers, and consumers, making for a healthier space overall. While some API provider are good at keeping developers in tune with documentation changes, not all of us are able keep up, and sometimes developers just aren't tuned in, and the API ChangeLog helps fill in the gaps.
Without outside access to API resources (like your docs), services like API ChangeLog do not exist, leaving developers to fend for themselves, and not providing valuable industry data that can be used by anyone. Services like API ChangeLog will be the lifeblood of the API economy, and provide valuable exhaust that informs API driven markets as they grow, and help give these markets som e of the positive forces they are so well known for.
Keep your APIs, and much of their supporting building blocks as accessible as possible, and while you are at it, make sure and index them using APIs.json, helping services like API ChangeLog provide vital data to developers, and the wider API economy.
