When to create an extension

Well, first you have to understand that extensions are all about togetherness. Once the objects from a contrib module were installed, PostgreSQL provided no way to show a relationship between them. This led many developers to create their own (and at times rather ingenious) methods to version, update, upgrade, and uninstall all of the necessary "stuff" to get a feature to work.

So, the first question to ask yourself when contemplating a PostgreSQL extension as a way to publish your code is "How does all of the 'stuff' in my extension relate together?"

This question will help you make extensions that are as granular as reasonable. If the objective is to enhance PostgreSQL with the ability to provide an inventory management system, it might be better to start with an extension that provides a bill of materials data type first, and subsequently build additional extensions that are dependent upon that one. The moral of the story is to...