So this option is many aspects similar to the default one, with one big difference. In this case each web server will have it's own db server.
Reason for this: Higher site availability; if one db server is down, second one can continue to serve customers. Also for this case load balancer must to be able to see both installations (this is some kind of prequel for cloud deployment).
On image you can see multiple web servers / db server but in general simplest option is to have 2 db servers.
Drupal 7 – Setup master-master replication with 2 MySQL db servers