The problem I had was when on-boarding with new development teams, myself & other developers were challenged with configuring our desktops & laptops to match the server's Ruby environment.
When I heard of Docker, I immediately downloaded at least ten images that day & became a big fan.
Docker solved my developer team woes in future by sharing my own projects as Docker images when necessary.
My favorite feature of Docker, is that it has allowed us to wrap virtually any server or client on the internet into a container and share it. Having has immediately saved days or weeks of on-boarding for myself & other developers who have joined teams I've been on.