Getting started with any distributed system that has several components expected to run on different servers can be challenging. Often developers and system administrators want to be able to take a new system for a spin before diving straight into a full-fledged deployment on a cluster.
All in one installations are a good remedy to this challenge. They provide a quick way to test a new technology by getting a working setup on a local machine. They can be used by developers in their local workflow and by system administrators to learn the basics of the deployment setup and configuration of various components.