Sure, maybe the metaphor doesn't make perfect sense.
...but, strictly, if you have a module with K public functions and P private functions the maximum possible number of unique external dependencies you have to track on the module is K.
If P > 0, then the 'api surface' of the module is smaller than the total set of functions.
If K = 0, the module has no external dependencies and you can do whatever you want.
I'm going to say with complete confidence that creating 'boxes' in your software where you minimize K creates maintainable software.
...but, strictly, if you have a module with K public functions and P private functions the maximum possible number of unique external dependencies you have to track on the module is K.
If P > 0, then the 'api surface' of the module is smaller than the total set of functions.
If K = 0, the module has no external dependencies and you can do whatever you want.
I'm going to say with complete confidence that creating 'boxes' in your software where you minimize K creates maintainable software.
When K = P, you have a dumpster fire.