[trustfundbaby]

Mostly answered already, but another use case is getting engineers up to speed on environments that they're not familiar with. For example, I work a lot with Rails apps, and sometimes we'll need a dev to come in and work some css/html magic or something like that. Well getting them setup with rvm, ruby, rails, bundler, mysql, elasticsearch and working through compilation errors on OSX can be a real nightmare, especially if you set up your env 2 years ago and have just been updating it incrementally since.

When we dockerize the app, they can be setup with the docker image and ready to go in under an hour, without having to screw with their system ... much.