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?