This is good, especially take time to read "Solved issues":
https://github.com/yarnpkg/rfcs/blob/1506ebf2865c157fc5b6d2b54f285a68acb798e4/accepted/0000-plug-an-play.md#4-solved-issues

It implements a system wide globally shared cache of npm packages and a
lookup-table in JavaScript which points to the cache.

This reduces install times, bootup-times and error cases.
https://twitter.com/arcanis/status/1040193511696609281