When it's not normal to use onRetainNonConfigurationInstance ()

The documentation onRetainNonConfigurationInstance()says, "This function is called pure optimization, and you should not rely on its call."

Under what circumstances onRetainNonConfigurationInstance()will not be called?

Some information about what I'm trying to achieve: I want my activitynotification to be orientationreliably changed (but also wants the activity to be killed and restarted, as usual).