why adding slashes before inserting into database

Hi:
i have a question about function addslashes(): why we need to format the
values(e.g String) with addslashes() before inserting into the database.

I have tried to insert data into db by doing these two different ways.
(1): with addslashes();
(2): without addslashes();
But i can not feel any difference.

Why?

 

www.php.net/manual/en/security.database.php

 

Have a look here:
http://www.php.net/addslashes

I Hope this helps.