Here's a post that an engineer on my team wrote about why we switched from NPM to Yarn

http://www.blog.distelli.com/single-post/2016/12/14/Why-we-s...

It's similar to Ruby's Bundler in that it uses a lockfile with a list of exact versions of dependencies. As a result, you get a more deterministic setup. At least that's the main benefit I see here.