The point of docker here is to make your dev environment the same as your production env as much as possible. If you develop on osx and deploy to linux sooner rather than later you will get bitten by env differences.
The biggest advantage of docker I've seen so far is Dokku [1]. If I want to get a dev-instance up and running to show to coworkers (or the client) I just can do "git remote add dokku dokku@example.com && git push dokku master" and share the link with them. And with very little modifications the same can be deployed at Heroku (though I don't use heroku personally).
And if you follow the dokku instructions it's fairly easy to setup, while doing something similar without Dokku but nginx/apache+php/passenger would take a fair amount of time to setup and config to run like that.
And if you follow the dokku instructions it's fairly easy to setup, while doing something similar without Dokku but nginx/apache+php/passenger would take a fair amount of time to setup and config to run like that.
[1] https://github.com/progrium/dokku