Is it necessary to have an ActionForm in Struts framework for any web Application?

It depends on your type of web application (static / dynamic).

It is mandatory to have an action form for a form submission and not required for link forward for example if we use
   its not necessary to have a form.
struts-config entry
 <action path="/logout" forward="/Logout.jsp"/>

It is not necessary to have ActionForm in the struts application if you are not using a form in ur html or jsp page but its is handy to have one if ur are submitting some data to the server using form.