The tips here are for advanced usages of composer and its assumed you have read about using composer and have a knowledge of your vendor packages to be updated. Let's consider, you want to update only one specific yii2 vendor library, without updating all the other extension packages?
There are scenarios when you work with DVCS (like Mercurial or Git) and CDbMessageSource. To my experience keeping the development database and production database in sync can be very time consuming. Plus, when working in a team, you never know when the database was updated.
There are some good guides out there explaining how to work with events and the ways to attach them to your components, but none (that I know) explain the following way to configure your events with CAction classes on your controllers the following way.