I'll give an example: I maintain a personal clojure/angular app for my girlfriend's students. One in a blue moon she asks me to fix things. Last time I reinstal

I'll give an example: I maintain a personal clojure/angular app for my girlfriend's students. One in a blue moon she asks me to fix things. Last time I reinstalled node, and the app was written against node 0.x, now node LTS is 6 or whatever, guess what, I couldn't even build it locally. Besides, I moved the app from a couple of VPSs (linode, DO, downsized it to cut costs, etc). But because I have my build dockerized, and it's running on docker too, I was able to quickly have an environment to run it. Although docker images are not exactly reproducible ( you do apt-get update and you can get different results), its good enough. For me, it boils down to isolation and reproducible systems.