At the moment it is pretty useless except you use simple $_POST['key']=stringvalue POST, GET not $_POST['key']=array. Sorry. It is a starting point of an idea - not tested in real life well: POST, GET sanitization, seems useful when someone is not sure if a website/app is protected against attacks.
Try to use it this way somewhere at the top of your page/application
if (!empty($_POST)) { $this->sanitizePost(); }
if (!empty($_GET)) { $this->sanitizeGet(); }