Box outlined how it used T3 to tame an unruly codebase that was maintained at first by a few engineers but ultimately needed dozens. T3 is meant to be a small piece of the overall architecture.
Those components cover services, modules and behaviors. T3 forces you to put your code and ideas into a category. Box maintains that everything it builds falls into one of those categories. T3 can also be used with other frameworks.
Generally speaking, T3 was created to enable collaboration, modular design and best practices.