Maybe for you. For others it can have all or any of those other things as its primary purpose. One important thing for me is that it prevents or at least mitigates unilateral insider attacks by having two people required to change code.
Having a bus factor>1 is still a major prerequisite for doing that. Because if you have a junior developer review the changes of a senior developer, there are so many social engineering tricks to make the backdoor pass the review that it isn't even funny.
