Perhaps because I'm primarily a coder, I don't understand the benefit of CI/CD, or any related terms such as scrum, agile, etc.

- In my opinion, testing can be done locally on development computer; 
- testing cannot replace manual code review, a lot of **security features are not easily tested** using automated scripts, there are lots of code paths whose functional correctness need to be examined, not to mention the many possible edge cases (speaking as a full-stack developer looking at back-end codes);
- the whole concept of CI/CD seem to be advertised towards managers and other non-coders, and generally for projects that aren't security-critical.

I've seen claims of benefit of CI/CD such as "faster xxx", "less bugs", "better code quality", etc. but except "faster xxx" (which I don't see why it's true), all other quality dimensions can be achieved though other means - style guide, use of linters, mentoring, etc.

So with all those said, what's the true benefit, application and non-applications of CI/CD?