Quoting the extract from official documentation (3.5 Restrictions):
Setting rendered="false" is OK when components are in the tree. However, if there are lots of components on a single view, for performance reasons some parts might be excluded by means of <c:if> or <c:choose> tags.
That's at least what could be done in 3.3.3. It worked fine back then. However, the JSF2 AJAX mechanism does not support this feature. This makes usage of aforementioned tags impossible in some cases.