Action form is somewhat a data transfer object used to collect the data from UI (done within the struts framework) and provide it in your Action Class and vise verse.
However, this turned to be one drawbacks in the Struts 1.x since most of the applications using struts (=>which follow the MVC model) already have similar domain objects to transfer data from action to data access layer (=>duplication and unnecessary code). This was not the case in Struts 2 (major of xwork). But I personally like it.
Have Fun with Java
little,little.. little by little makes a lot..