Multiple Database Connection

I m using three DBs on my company projects.  it is easy as 1,2,3.  Configure it from database.php

In the User Guide it says:
Connecting to Multiple Databases
If you need to connect to more than one database simultaneously you can do so as follows:
$DB1 = $this->load->database('group_one', TRUE);
$DB2 = $this->load->database('group_two', TRUE);

Is this to be placed in each model?

Please enlighten me with a more detailed explanation!!

Thanks in advance,
HEKuiper