public vs external functions

knowing that the external/internal functions do the following:
- External – Can be accessed externally only.
- Internal – Contracts within the system and contracts deriving from them can access.
aren't the external functions useless?
I mean, we can make a public function and not call it in the smart contract , if we do so , it becomes automatically external, right?
submitted by /u/iMnoTGudd
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