People always makes mistakes. Like forgetting to include a change. The point of PRs for me is to try to weed out costly mistakes. Automated tests should hopefully catch most of them though.
The point of PRs is not to avoid mistakes (though sometimes this can happen). Automated tests are the tool to weed out those kinds of mistakes. The point of PRs is to spread knowledge. I try to read every PR, even if it's already approved, so I'm aware of what changes there are in code I'm going to own. They are the RSS feed of the codebase.
