How important is it for a software product to have an API?
@evan
I work since 30 years in software development area and everything needs an API. Btw., we distinguish between private, protected and public API and I guess you mean the public one.
A public API is very important if you pass control over input, output or configuration to the consumers. It takes effort to maintain it (because it's a second interface beside your main frontend), but it's a worthwhile investment in customer loyalty.
So yes, very important.