1. Web Designer never has to touch Java code;
2. Create multiple "Web Skins" for a application;
3. Change Look and Feel;
4. Change Layout on a given Web Page;
5. Change Flow among Web Pages;
6. Move *existing* data elements from one page to another;
7. Integrate with various backend infrastructures;
8. Reuse components;
9. Perform internationalization (i18n) of a web application;
10. Keep the API small and to the point;
11. Ability to learn WebWork fast, by making all the fancier features optional;
12. Allow the developer to choose how to implement as much as possible, while providing default implementations that work well in most cases [1];

I'm not sure if the order on the list above reflects the priority but if so I would strongly use the items from 8 until 12 as the first top one priorities:

1. Reuse components;
2. Keep the API small and to the point;
3. Ability to learn <YOUR FRAMEWORK/API NAME HERE> fast, by making all the fancier features optional;
4. Allow the developer to choose how to implement as much as possible, while providing default implementations that work well in most cases [1];
5. Perform internationalization (i18n) of a web application;

An the last item is for certain one of the main strengths of the Springframework, as well as the terrific usage of Object Oriented advantages as Polymorphism.

I stumble upon this WebWork article because a tool I'm using for the past months makes some use of it :)