hasMany中的独家选项是什么？

In cakephp, there is an option called "exclusive" in "hasMany" field in models. The documentation says:

When exclusive is set to true, recursive model deletion does the delete with a deleteAll() call, instead of deleting each entity separately. This greatly improves performance, but may not be ideal for all circumstances.

But it is not so clear. I want to know what does this option do exactly, and what happens if we don't use it? Thanks.

Say For Example, One Author has many Books.So we can write this in form of $hasMany association as below,

   var $name = 'Author';
       var $hasMany = array('Book' =>
        array('className' => 'Book',
            'conditions' => '',
            'foreignKey' => 'author_id',
            'dependent' => true,
            'exclusive' => true

        )
    );

dependent: When dependent is set to true, recursive model deletion is possible. In this example, Book records will be deleted when their associated Author record has been deleted.

exclusive – If set to true, all the associated objects are deleted in one SQL statement without having their beforeDelete callback run.This greatly improves performance, but may not be ideal for all circumstances.

Now just look at the records in the database

authors table
===================
id    name    
===================
1     first author
2     second author 
3     third author

books table

==================================
id   title   isbn       author_id
==================================  
1    abc    6416446846   1
2    xyz    3146354313   1
3    pqr    8945468485   2
4    fgh    6434164656   2
5    rtt    1215445644   3

Now if you delete any record of Author,all the associated books with that particular Author will also be deleted.