The only thing penance does for the penitent is make them feel good about himself.
It literally, has no redeeming value.
It’s a useless waste of time.
If the person is saved, it does nothing to add to salvation.
If they are unsaved, it does nothing to bring about salvation.
This is why we don't see saints in heaven doing penance. But we on this earth are not saved yet, despite what your Protestant theological fantasy teaches.