Granularity of Use Cases

I have seen many newbies struggle with a basic question of how granular use cases should be. I will try to address that question in this post.

Conventional wisdom as articulated in various books [Use Cases: Patterns and Blueprints] and articles [Use and Abuse Cases] argues that functional decomposition of use cases to derive smaller, more fine grained use cases is bad, if taken too far. Most literature is concerned with preventing the “explosion” of use cases.

How far is too far? What is “explosion”? The answers to these questions are tied to another question – “what do you intend to do with your use cases?”