Both the command line interface and the webpack loader are wrappers around the core library, handling implementation details such as the output location, live information and output manifest generation.
If you need a little more control over the IPP implementation, you can write your own wrapper/adapter that uses the code library, while still abstracting away the image processing details.
An excellent use-case for this is server-side image processing in a serverless environment. It can scale to any number of image jobs, and you only pay for the time spent processing (although serverless is generally more expensive than raw compute resources, assuming your compute is used with perfect efficiency). Most serverless function providers feature Node.js as a first class runtime, simply add IPP to your dependencies and call the interface with your image data. The rest is up to you.