As I see, your setup is for system users. This is good if you are not going to deal with big number of users.
You can also try a setup for virtual users and domains. There are many related Howtos on this site.
About the advantages, see what Falko
says in one of his howtos:
The advantage of such a "virtual" setup (virtual users and domains in a MySQL database) is that it is far more performant than a setup that is based on "real" system users. With this virtual setup your mail server can handle thousands of domains and users. Besides, it is easier to administrate because you only have to deal with the MySQL database when you add new users/domains or edit existing ones….