A language like ocaml excels when the input and output are program-like, and the problem can't be number-crunched by hardware. The typical example would be a compiler. Other examples would be model checkers, code generators for number crunching libraries, proof assistants, and so on. Complex problems, where you need to explore different avenues of approach quickly, and where symbolic manipulation is at the heart of the problem.

Thus, ocaml is best used as a "kernel" or "module". The contextual part of your system uses the part written in ocaml as a service.

But ocaml doesn't excel at problems which are common to a typical company. The people who are in the intersection of wanting to solve those problems, and ocaml developers are few. The same intersection with a more mainstream language is far larger.

However, if you find yourself with a problem at which ocaml excels, chances are the mainstream languages ends up falling short very quickly, because they tend to lack the abstraction features necessary for correctly handling the complexity.