Why is the rails_12factor gem necessary on Heroku?

Question

I noticed that the new version of Michael Hartl\'s Ruby on Rails Tutorial says to include the following to serving static assets on Heroku

gem \'rails_12facto

Answer 1

This gem enables serving assets in production and setting your logger to standard out, both of which are required to run a Rails 4 application on a twelve-factor provider. The gem also makes the appropriate changes for Rails 3 apps.