As a freelance fronted dev, I really love Docker. I don't need to mess up my system installing ancient Java versions or whatever Python wants to easy_install, pip or whatever, I can just run the backend Docker image and go on with my life. Especially when project A's backend has incompatible Java/Ruby/Python dependencies with project B.

You can shit on npm all you want (yes, I was there for left_pad), but at least they got the dependency issues between projects solved.