Sprintf in itself will not secure a MySQL query from head to toe. That should be made clear from the word go. There are many more techniques that go into ensuring a MySQL statement is safe to execute on the MySQL server. Sprintf will, however, take a lot of the sting out of any malice.
Not only will your new found knowledge help you when it comes to security, but sprintf and its twin brother with a slight genetic mismatch, printf, are on hand to make your PHP code look a lot more programmer-friendly.