No harm in adding it, but it is a meaningless option as of 2021, since it has been the default behavior since npm@5 in 2017.
npm installsaves any specified packages intodependenciesby default. Additionally, you can control where and how they get saved with some additional flags: …
--no-save: Prevents saving todependencies. https://docs.npmjs.com/cli/v6/commands/npm-install
Breaking Changes npm will —save by default now. Additionally, package-lock.json will be automatically created unless an npm-shrinkwrap.json exists. https://blog.npmjs.org/post/161081169345/v500
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