Trees. Big trees. Little trees. Elaborate trees. Simple trees. While they come in many shapes and sizes, they are all useful. Multinomial Processing Trees are no exception to this. For example, they have been used in a wide range of applications such as grading the SAT exam, to measuring latent variables in psychology. Well, what makes them so darn popular? Simplicity. For starters, they are easy to implement. They are also very flexible, allowing them to be used for many different paradigms. And generally good all around models.
In the psychological sciences we use them for mapping external observations to internal latent cognitive variables.