Some commands like npm install has a --production flag, which when used makes npm to install only dependencies listed in dependencies and not in devDependencies sections of the project manifest.
Here's the description of this flag from documentation:
With the --production flag (or when the NODE_ENV environment variable is set to production), npm will not install modules listed in devDependencies.
However, what are the practical applications of this flag?
It can be used only when npm install is issued inside of the project directory, probably obtained by cloning a Git repository. Otherwise the package would be installed via npm install package-name and it would be automatically installed without devDependencies.