If you write JavaScript or TypeScript, you already know the feeling: a dozen old project folders, each carrying a node_modules directory that's 200 MB to several gigabytes, and together using 20–60 GB you could easily get back. node_modules is one of the biggest space users on a developer's machine, and it's easy to miss — buried several folders deep, where you'd never think to look.
Every project installs its full dependency tree locally. Transitive dependencies multiply, native build artifacts get cached, and nothing cleans up after itself. A repo you haven't touched in eight months still has its entire node_modules sitting there. Multiply that across every side project, every cloned repo, every tutorial you followed once, and the number gets large fast.