GO provides an attractive GUI that lets you see your build and deployment history or trigger manual deployments. When did you last deploy to live? what git commit did you deploy? who deployed it? GO helps you to answer all of these questions very easily.
When it comes to running tasks, like tests, delegating to Docker removes a whole category of installation and configuration headaches. All I need to install on a GO agent is Docker - any dependencies needed by an application are installed within a container. You never need to touch the host OS.