preRenderView is a JSF specific event which is triggered right before the render response phase
<f:event type="preRenderView">
is a JSF specific event which is triggered right before the render response phase.
It enables developers to attach listener methods which run right before the first bit to the HTTP response is been written, so that any necessary preprocessing could be performed which may be significant for the shape and the state of the response (e.g. preloading some presentation data or even a redirect).
It's often been used in combination with <f:viewParam>
as workaround to trigger GET actions based on view parameters, because no suitable "GET action listener" tag exists in JSF 2.0/2.1. This is in JSF 2.2 solved by the new <f:viewAction>
tag.