Why set variables inside the construct of a PHP class when you can set them when they are declared?

Is there a reason to set a value for variables in the constructor of a class rather than when you declare them? I realize you can't pass data into the variables if you try to set them when they are declared, but what about things that will always be the same ( i suppse 'always' is a tough claim to make )?

class variables_set_outside_constructor
{
     private $admin_name = 'jeff';
     private $current_working_directory = get_cwd();

     function __construct() {}
}

as opposed to this:

class variables_set_inside_constructor
{
     private $admin_name;
     private $current_working_directory;

    function __construct()
    {
         $this->admin_name = 'jeff';
         $this->current_working_directory = get_cwd();
    }
}

What are the advantages and disadvantages of settings values in the constructor versus when they are declared? I'm curious about any language agnostic aspects as well.