When executing your template, CloudFormation will automatically work out which resources depend on each other and order their creation accordingly. Additionally, resource creation is parallelized as much as possible so that your stack execution finishes in the timeliest manner possible. Things occasionally become unstuck, however.
Let's take an example where an app server depends on a DB server. In order to connect to the database, the app server needs to know its IP address or hostname. This situation would actually require you to create the DB server first so that you can use Ref to fetch its IP and provide it to your app server. CloudFormation has no way of knowing about the coupling between these two resources, ...
