One of the use cases where a tool like the API Designer creates huge value is for vendors that have a wide range of products acquired at different times.
Trying integrate these solutions and get synergies between them is very difficult. Using traditional software development techniques it can be very time consuming for APIs to be developed. A large part of the challenge is that the technical teams developing the APIs often are not best qualified to understand the needs of customers when it comes to the final integrations.
The API Designer makes building these APIs much more transparent and accessible to people who are closer to customers and then gives a common tool chain for large organizations to quickly mobilize and build out APIs on multiple products in parallel at a much faster rate with less cost that can be achieved using more traditional options.
This is exactly what Jeff Bezos did with Amazon by insisting on that every team expose their data via APIs, but an order of magnitude less expensive with a quality of APIs that are much easier to use and understand.