The answer to this question depends on what your usage of PHP is. If you are using PHP only for your own server and only for your own scripts and applications, then you can judge for yourself, if you trust your code enough. In that case you most probably don’t need some of Hardening-Patch‘s features, that are meant to protect servers against vulnerable programming techniques. However there are some features like the Zend Engine Protection features, that protect your server from possible bufferoverflows and related vulnerabilities in the Zend Engine. History has shown that several of these bugs have always existed in previous PHP versions.
Answering the question is even simpler if you are not only running your own PHP scripts but are hosting 3rd party PHP applications for yourself or even for possible customers. In that case you most probably cannot trust the code quality of the PHP applications you use. History has shown, that many holes exist in PHP applications. Even educated PHP programmers have stepped into one of the pitfalls of the PHP language before. The Hardening-Patch has many built-in features that protects against those pitfalls of the PHP language, that sometimes even kill whole classes of security holes, when they are turned on.
Summed up, it is your free choice if you want additional protection for your servers and your business. We can only recommend strongly, that you use the patch, because you are not only protecting yourself, but also the internet itself, by ensuring one more server is a lot harder to be turned into an attack drone.