What it does is that it restores state of rendering a form.
For example I had this form:
 <s:validateAll>
 <h:message for="name"/>
 <h:outputLabel for="name" value="Grupi nimi"/>
 <h:inputText id="name" value="#{category.name}" styleClass="field"/>
 <h:message for="head"/>
 <h:outputLabel for="head" value="Tüvikategooria"/>
 <h:outputText id="head" value="#{category.head.name}" styleClass="field"/>
 <h:message for="showed"/>
 <h:outputLabel for="showed" value="Avalik"/>
 <h:selectOneRadio id="showed" value="#{category.showed}" styleClass="field">
 <f:selectItem itemValue="true" itemLabel="Jah"/>
 <f:selectItem itemValue="false" itemLabel="Ei"/>
 </h:selectOneRadio>
 <s:link view="/haldus/mcategory.xhtml" id="submit" value="Loo grupp" action="#{cateditor.create}"
 buttonClass="button" linkStyle="button"/>
 </s:validateAll>
and after submiting it, it restored category, so the name became null.