npm scripts allow developers to create custom CLI tools and automate tasks in their Node.js projects. They can be used to set up build, dev, or start scripts, as well as perform pre- and post-scripts that can chain commands together without convoluting the script. Environment variables are also augmented when running a command or script through npm run..., providing access to general npm configuration and project-specific settings. Argument passing and parsing can be done using two methods: directly passing arguments to the actual command, or using npm's built-in argument parser. Useful tools such as rimraf, ncp, npm-run-all, cross-env, and others can help bring npm scripts to the next level by providing additional functionality for tasks like deleting build artifacts, running linters before tests, and working with environment variables across platforms.