Never ever use references in PHP just to reduce memory load. PHP handles that perfectly with its internal copy on write mechanism. Example:
$a = str_repeat('x', 100000000); // Memory used ~ 100 MB $b = $a; // Memory used ~ 100 MB $b = $b . 'x'; // Memory used ~ 200 MB
You should only use references if you know exactly what you are doing and need them for functionality (and that’s almost never, so you could as well just forget about them). PHP references are quirky and can result to some unexpected behaviour.