Inversion of control for modularity and testability.
The IoC container at the core of Spring libraries will help you write more modular software. The end result will be more reusable, maintainable and testable applications.
Code portability through decoupling and the rich toolbox of features in Spring make it easy to forklift applications from the local development environment into any web container and cloud platform.
The full set of Spring libraries available.
Spring is not just about @Autowired and IoC. The really handy Spring libraries, like the awesome Spring Data, are helpful in typical Vaadin applications as well.