It's an Erlang convention. Erlang suffers from having a very rudimentary module system, so a clean separation between the public API and the gen_server API isn'

It's an Erlang convention. Erlang suffers from having a very rudimentary module system, so a clean separation between the public API and the gen_server API isn't that easy to make. If you have access to a better module system, you should definitely induce a cleaner separation and adapt that as a convention. It helps people in general, but the in particular the less experienced.