Honest question: what are the benefits of using environment variables over having an actual configuration file (that is obviously not added to version control) ?
Unless your environment demands it, it doesn't matter. In fact, it can be a bit of a pain in the ass to implement on your own, if you are not using Heroku or some such. The main point there is to not put secrets into your git repo. How you accomplish that for the most part doesn't matter.
Heroku & Docker.
But most importantly, it lends to dynamic configuration when using etcd or zookeeper.