The short answer
The API layer is where the real magic happens. The API allows
programmers to easily interact with external electronic components
through a simple intuitive library. The difficulty of I/O communications
is now gone. The I/O boards and controllers with their drivers and API
handle the entire process for you. This leaves developers and
programmers free to concentrate on what they do best, writing code.
The long answer
You have probably read out mission statement by now: