A Value object or data transfer object (DTO) is a Plain Old Java Object (POJO) that is used to transfer information between the model layer and the view layer. An ActionForm belongs strictly to the view layer, and acts as a Java representation of an individual JSP page.
One might think "Hey, these two objects look similar. Why not just use the ActionForm as a DTO?"
This is not a good idea. Using an ActionForm as a DTO introduces a dependency on Struts into your Model layer. Model objects should maintain independence from any type of view logic or view platform.