what is CakePHP model alias used for?

In user model:

var $hasMany = array(
        'Photo' => array(
            'className' => 'Photo',
            'foreignKey' => 'owner_id',
            ...
        ),
);

In photo model:

var $belongsTo = array(
        'Owner' => array(
            'className' => 'User',
            'foreignKey' => 'owner_id',
            ...
            ),
);

Here one user has many photos. So what my question is that here the alias name is 'Owner', which make me clear to understand the exact meaning of 'User', but is this the only reason to use alias? does it affect 'Photo' in user model? or how to use 'Owner' in/by cakephp?

I don't quite understand the meaning of alias in model. Appreciate your help!