I noticed that in 95% of cases there is always just return; after evaluating zend_parse_parameters to FAILURE inside PHP_FUNCTION. It did not make sense because PHP_FUNCTION are expected to return ZVAL. I am not sure what default value of return_value is when it is not explicitly set.
I searched through all php sources and all extension sources that came bundled with php. In 95% of cases they simply used return. In few extensions - date and intl they do RETURN_FALSE. In an article written by Sara Colemon she used RETURN_NULL().
I feel strongly that I should be using RETURN_FALSE for most cases which make more sense for PHP_FUNCTIONs. Am I missing something somewhere?