PHPStorm inspections and external quality tools

I've been looking at the options for integration with external quality tools. The application of CodeSniffer and CS_Fixer are clear to me, as they can apply and fix coding style rules specific to a project. What's less clear to me is what advantages external static analysis tools like PHPStan, PHP mess detector and Psalm offer over PHPStorm's own built-in inspections.

If you are using integration with one or more of these tools, would you mind sharing the "killer features" for you that make integrating with an external tool worthwhile?