[Caml-list] Why should I use .mli files?

[Francois Berenger <berenger@riken.jp>]

Hello,

Here is my stupid question of the day:
what's the use of those .mli files?

Is it just to separate interface from implementation
so that the implementation of a module can be changed
without clients of its interface to have to bother?

Does it make compilation of large software faster
by allowing for more parallelization and maybe later on avoiding to 
recompile some parts?

Usually I program in a pure functional style, so my modules
don't carry an internal state.
I feel like "if someone want to re-use a function, so be it".
If I really want to hide a function that I am afraid people
may call in an incorrect manner, I declare it internally
to some public function and use it correctly.

Also, maybe I only work on toy-size OCaml projects. So, I never 
bothrered to create any .mli file.
I would like to know if I should bother about them.

Thanks a lot,
Francois.