pnpm uses hard links and symlinks to save one version of a module only ever once on a disk.
When using npm or Yarn for example, if you have 100 projects using the same version
of lodash, you will have 100 copies of lodash on disk. With pnpm, lodash will be saved in a
single place on the disk and a hard link will put it into the
node_modules where it should
As a result, you save gigabytes of space on your disk and you have a lot faster installations!
If you'd like more details about the unique
node_modules structure that pnpm creates and
why it works fine with the Node.js ecosystem, read this small article: Why should we use pnpm?