I don't think it matters as long as the method call handles the variable as a reference. As a code example:
PHP:
<?php
class A
{
public function verifyThing(&$value)
{
$value = 'abc';
}
}
$a = new A();
$value = '123';
$a->verifyThing($value);
\XF::dump($value); // value is 'abc'
It's more strict when using call_user_func_array because the validation of what parameters are expected is stricter.