A Guide for Upgrading Ruby on Rails — Ruby on Rails Guides

Autoloading is now disabled after booting in the production 
environment by default.


For the vast majority of applications this change needs no action. 
But in the very rare event that your application needs autoloading 
while running in production mode, 
set Rails.application.config.enable_dependency_loading to true.

これは必要なタイミングで個別に require すべしということなんでしょうか?
基本は app 以下に配置すべきということなんでしょうかね。