To be honest, there isn't any, when I implemented it I was the tender age of 16 and thought there was some validity in the method, but in itself, once you get to these kind of 30-ish letter long passwords, they become damn near impossible to brute force.

The only redeeming factor I suppose would be that you have to store your random string somewhere anyway, at least this method required code traversal rather than just an SQL field named "password_salt".